SeqLine Bio · How to verify a supplier
Buyer guide · supplier due diligence
How to verify a peptide supplier before you pay
Eight checks that work for any supplier, in the order you meet them, from the first quote to the first repeat order. Each step links to a guide with more detail.
The method
Eight checks, in order.
Ask for every answer in writing. A supplier that answers clearly at step 1 usually answers clearly at step 8.
- State the roleAsk whether the company is the manufacturer, a stockist or a trader for this lot. The answer should match the website, quotation and invoice. See manufacturer vs reseller.
- Match the namesThe company name and address on the website should appear on the quotation and proforma invoice. Ask about every name that differs.
- Get the lot COAAsk for the COA of the lot you would receive, not a sample report. Compare product, strength and lot number with the quote. See current-batch COA.
- Read the COACheck HPLC purity against the stated specification and the MS mass against the expected molecular weight. See COA, HPLC and MS explained.
- Check the payeeThe beneficiary on the payment instruction should be the contracting entity. A personal account, or bank details sent only by chat, is a reason to stop.
- Order small firstA sample order tests the material, packaging, lead time and communication at low cost.
- Test it yourselfSend part of the received material to a lab you choose, and agree beforehand what happens if it misses the specification. See independent testing.
- Re-check every lotEach repeat lot needs its own COA. Match the lot number on every shipment, not only the first.
Warning signs
When to pause the order.
A sample report sold as the current lot, lot numbers that don’t match, a payee that differs from the seller, or pressure to skip testing. Each is a reason to ask one more question before paying.
Applying this to SeqLine Bio
Run the same checks on us.
We are a research peptide manufacturer in Guangzhou. Our quotation names the contracting entity, payee, production site and releasing QC for your order. Every published lot has a public COA in the COA library, and sample orders start at 1 kit (10 vials).
FAQ
Questions buyers ask.
Is the supplier’s COA enough on its own?
No. A COA is the supplier’s own record. It counts when its lot number matches the material you receive, and it is stronger when your own test agrees with it.
What should I ask for before payment?
A quotation naming the seller, the COA for the lot you would receive, a proforma invoice whose payee matches the seller, the delivery terms and the quality-claim terms.
Can I test a small order first?
Yes, and you should. Most suppliers sell sample quantities. At SeqLine Bio a sample order starts at 1 kit (10 vials) for most catalog compounds.
Next step
Send your compound list and document requirements.
We reply within 4 business hours with price, lead time and the COA for the lot you would receive.