Most supplier switches fail in the first 90 days for the same reason. The procurement team ran a clean RFQ, picked a vendor on unit price, and discovered after the first production order that the dimensions were off, the lead time slipped, freight wasn't quoted, or there was a 5,000-piece minimum hidden behind the headline price. The story ends with parts in a bonded warehouse and the buyer reaching back out to the incumbent.
That story is avoidable. Buyers who consistently bring in good new suppliers ask a structured set of questions during evaluation and treat the answers as a filter, not a formality. This guide is that filter -- 15 evaluation questions plus sections on MOQ structure, lead time verification, sample policy, certification, TCO math, and red flags in the quote document itself.
Why Most Supplier Switches Fail
Supplier switches usually fail because the evaluation focused on the wrong variables. The common failure mode: the buyer compares unit prices across three quotes, picks the lowest, places a production order at minimum quantity, and discovers the unit price was the smallest of the actual costs.
Hidden costs that show up after the order include EXW freight terms instead of DDP, packaging that does not match your intake, tolerances inside the supplier's envelope but outside your fit window, lead times that slip 2 to 4 weeks past the quoted date, and quality escapes you only catch on the floor. None are visible in a unit price comparison. Successful evaluations start with a sample, confirm lead times against a real production calendar, verify the MOQ is not a stretch ceiling, and price the total relationship over 3 years.
The 15 Questions That Actually Matter
Print this list. Bring it to the next supplier qualification call. If a supplier cannot answer any of these in plain language without escalating, that is itself a data point.
- What is your sample policy on a new part -- cost, lead time, and how many revisions are free?
- What is the actual MOQ on this part, and is it a hard floor or a negotiation point?
- What is the lead time for the first production run, and what is the reorder lead time after approval?
- Where is the part actually manufactured, and if through a partner network, how are the partners qualified?
- What material certs, mill certs, or data sheets ship automatically with each lot?
- What dimensional inspection happens before parts ship, and what documentation comes with the shipment?
- What is your OTD rate for the past 12 months, and against which date is it measured?
- What are your freight terms, and is freight included in the unit price or quoted separately?
- What are your payment terms on a first order vs. repeat orders, and do you require deposits?
- What happens if a production run is rejected at incoming inspection -- replacement timeline, RMA, responsibility?
- Do you warehouse approved inventory for repeat customers, and what is the reorder lead time from stock?
- Who is my single point of contact for quoting, expediting, and quality, and what is the response commitment?
- If specs change mid-program, how is a running change handled, and is there a re-tooling or re-sample charge?
- Will you sign an NDA before I share drawings, and how is customer IP protected across the partner network?
- Can you give me references from two customers in my industry running at my volume?
Use the answers as a filter, not a formality
The point is not to grade suppliers on a rubric. It is to expose mismatch between what the supplier sells and what you need. If the answer to question 2 is "we can probably work with you on the minimum" instead of a number, that is the start of a renegotiation you will lose later.
MOQ and Quantity Terms
MOQ is where the largest gap between quoted price and real price hides. A great unit price at "1,000 piece minimum" can become a worse deal when the minimum applies per SKU, per color, per packaging configuration -- and a 6-month buffer is actually 6,000 pieces upfront.
Nail down three things in writing. Is the MOQ a hard manufacturing floor (tooling economics) or a sales floor (supplier preference)? Does it apply per shipment or per part number across a release schedule? What is the MOQ on the second order? Suppliers who warehouse approved inventory for repeat customers can usually accept much smaller reorder quantities -- sometimes a single box.
Lead Times: What to Verify vs. What to Take on Faith
Lead time is the second most-misrepresented number in supplier quoting after MOQ. Sales teams quote optimistic lead times. Production schedules slip. Freight estimates assume best-case routing. By the time parts hit your dock, the original quoted date is a memory.
Verify two things. Is the quoted number a manufacturing lead time or a door-to-door lead time? A 35-day manufacturing time becomes 50 days door-to-door once you add freight, customs, and consolidation. And what is the supplier's on-time delivery rate over the past 12 months, measured against the original quoted date (not a renegotiated one)? Realistic first-order ranges: 21 to 35 days for standard hardware and stamped parts, 28 to 45 days for custom brackets, 30 to 50 days for custom rubber and brush seal runs, up to 45 days for more complex parts.
| Dimension | Good | Red flag |
|---|---|---|
| Sample policy | Free sample on production tooling, unlimited free revisions to QC pass. | Tooling charge upfront, catalog swatch, billable revisions, vague lead time. |
| Lead time transparency | OTD measured against original quote, manufacturing and door-to-door broken out. | OTD against renegotiated dates, freight time ambiguous, no committed ship date in writing. |
| MOQ structure | Hard floor explained in tooling terms, second-order minimums in writing. | MOQ described as flexible, no second-order minimum, surprise re-quote on the second PO. |
| Material documentation | Mill certs and data sheets automatic with shipments, traceable to specific run. | Certs on request, no traceability, generic material claim with no data sheet. |
Sample Policy as a Filter
The most useful filter in supplier evaluation is the sample policy, precisely because it is hard to fake. A supplier willing to manufacture a verification sample on production tooling for free and revise it at no cost until it matches your spec is putting real money behind their confidence. A supplier who quotes a tooling charge upfront or sends you a catalog swatch is telling you how they view the relationship.
Want on the sample line: zero cost on the first verification sample, manufactured to your exact spec on production tooling, unlimited free revisions, and 3 to 7 day turnaround. If any is missing, ask why. There may be a legitimate reason (exotic material, oversized part, dedicated new tooling) but there should be a clear explanation. When the sample arrives, measure it on a CMM, check durometer with a gauge, put it in your actual assembly. The sample is the cheapest insurance policy in custom component sourcing.
Certifications and Quality Documentation
What certifications mean: a quality system audited against a standard. ISO 9001 covers design control, production control, inspection, and corrective action. AS9100 layers aerospace requirements on top. IATF 16949 layers automotive requirements on top. These matter where the end customer requires certified suppliers in the chain.
What certifications do not mean: that the parts are good. Plenty of certified suppliers ship bad parts and plenty of uncertified suppliers ship excellent parts. The certification is a structural indicator, not a quality guarantee. The more practical question is what documentation ships with each lot: material data sheets for the polymer or alloy, mill certs or batch certs for raw stock, dimensional inspection records for sampled parts, and a packing list that ties the shipment back to a specific production run. That is what your QA team actually uses at incoming inspection.
Certification scope can be narrower than you think
When a supplier says they are ISO 9001 certified, ask which facilities and product categories the certificate covers. A supplier may hold a certification on one facility or product line and not on the operation that will actually run your part. Get a copy of the certificate and read the scope statement.
Total Cost of Ownership, Not Just Unit Price
Stop comparing unit prices and start comparing total cost of ownership over a 3-year horizon. TCO includes unit price, freight (5 to 15 percent of unit cost on international sourcing), carrying cost on safety stock (15 to 25 percent annually on average inventory value), expediting when the supplier slips, quality failure costs (rework, scrap, line stoppages, end-customer returns), and switching costs if you have to replace the supplier mid-program.
A 12 percent unit price savings looks like a clear win until you add the hidden costs. If the new supplier requires 6 months of safety stock (versus 1 month on the incumbent), that 12 percent can be entirely consumed by carrying cost. Suppliers who warehouse approved inventory shift the math: reorder lead times of 1 to 2 weeks instead of 6 to 8 weeks make the unit price savings real instead of theoretical.
Red Flags in the Quote Itself
Scan the quote document before you talk to anyone. Validity period under 30 days (confident suppliers hold 60 to 90 days). Specs echoed back vague instead of confirmed. No freight terms (EXW, FOB, FCA, DDP missing -- freight can shift unit cost 10 to 20 percent). Deposit on a first standard production order (tooling deposits can be legitimate, production deposits are a question). No reference to a verification sample. Boilerplate quality language with no specific OTD, first-pass yield, or RMA numbers -- if they cannot give you numbers, they do not measure them.
If you only do one thing from this guide
Refuse to place a production order with a new supplier without holding a verification sample first. The sample is the cheapest insurance policy in custom component sourcing, and any supplier who pushes back is telling you something about their confidence in the part.
Frequently Asked Questions
How long should a normal supplier evaluation take?
Allow 4 to 8 weeks from first contact to approved verification sample. Quote turnaround on a clean RFQ should be 24 to 72 hours, sample lead time 3 to 14 days, internal QC review a few days. If a supplier drags past 8 weeks without a clear reason, that pace will repeat on every reorder.
What is a fair sample cost on a custom part?
For standard custom components -- brushes, seals, brackets, fasteners, idlers, roller tubes, stamped parts -- the fair cost on a first verification sample is zero, including unlimited free revisions. For exotic materials needing dedicated new tooling, a nominal upfront contribution is sometimes legitimate. A four-figure sample charge on a standard part is a signal to run a second-source quote.
How do I verify a supplier's stated lead time before I commit?
Ask for the OTD rate over the past 12 months and how it is measured (original quoted date vs. renegotiated). Ask whether the quoted number is manufacturing time or door-to-door. Then verify on the first order by tracking actual ship date against quoted date. The first PO matters more than any reference call.
Should I require ISO 9001 certification on every custom component supplier?
Only if your end customer requires it. Otherwise, focus on the documentation that ships with the parts: material data sheets, mill certs, dimensional inspection records, and traceability to specific runs. That is what your QA team actually uses, and it is often available from non-certified suppliers as well.
What is the right way to compare two quotes with different unit prices and lead times?
Build a 3-year TCO model: unit cost, freight, carrying cost on the safety stock each supplier's lead time requires, and an expediting reserve for the supplier with the longer or more variable lead time. Suppliers who warehouse approved inventory usually have shorter effective reorder lead times, which shifts the comparison in their favor.
How do I know if a supplier is real or just a broker reselling someone else's parts?
Ask where the part is manufactured, who manufactures it, and how the supplier qualifies and audits their partners. There is nothing wrong with sourcing through a partner network -- it is how most custom component supply chains work -- but the supplier should be able to describe the structure and quality verification. Vague answers are a red flag.
Run this checklist on us first
If you are evaluating SB5 as a new custom component supplier, ask us every question in this guide and grade the answers honestly. Then ask for a free verification sample before you place a production order. We will quote in 24 to 48 hours, ship a sample on production tooling, and revise at no cost until it passes your QC.