After 3 years in the peptide community and a few expensive mistakes, I've developed a systematic checklist for evaluating new vendors. Sharing it here because I see too many people ordering based on price alone.

The DueDiligenceDave Vendor Vetting Checklist:

TIER 1 — Deal Breakers (instant rejection if any fail):

• [ ] Website age > 6 months (check WHOIS)
• [ ] Accepts credit cards or PayPal (not crypto-only)
• [ ] Provides batch-specific COAs (not generic)
• [ ] Has at least 5 independent reviews with lab results
• [ ] Responds to customer service inquiry within 24 hours

TIER 2 — Quality Indicators (want 4/5 minimum):

• [ ] Third-party COA (Janoshik or Finnrick) available for current batches
• [ ] Ships with cold chain packaging
• [ ] Provides lot number and expiration date on vials
• [ ] Has a published return/reship policy
• [ ] Active community presence (forums, not just social media)

TIER 3 — Premium Indicators (nice to have):

• [ ] Endotoxin testing on COA (not just HPLC purity)
• [ ] Sterility testing documentation
• [ ] Published reconstitution guidelines
• [ ] US-based with verifiable address
• [ ] Consistent pricing (no wild fluctuations)

This is excellent. I'd add a few more items to the checklist:

TIER 1 additions:

• [ ] No fake Janoshik/Finnrick COAs. Always email the lab directly to verify. Both labs will confirm or deny a report number within 24 hours. I've caught two vendors with fabricated reports this way.
• [ ] No "FDA approved" or "pharmaceutical grade" claims. No compounding vendor is producing FDA-approved semaglutide. If they claim to be, they're lying about their regulatory status.

TIER 2 additions:

• [ ] Peptide content testing (not just purity). HPLC purity tells you what percentage of the peptide is semaglutide vs impurities. But it doesn't tell you the total amount of peptide in the vial. A vial labeled 10mg might only contain 7mg of total peptide at 99% purity — that's 6.93mg of semaglutide, not 10mg.
• [ ] Ask to see their LC-MS/MS identity confirmation. HPLC alone confirms purity but not necessarily identity. LC-MS/MS confirms the molecular weight matches semaglutide.

Former pharma QC analyst here. A few technical additions:

What to look for on a COA:

1. HPLC method details: A legitimate COA should specify the column type (usually C18), mobile phase, flow rate, and detection wavelength (typically UV at 214nm or 280nm for peptides). If the COA just says "HPLC: 98.7%" without method details, it's less credible.
2. Reference standard: Was the test run against a certified reference standard? Janoshik and Finnrick both use USP or EP reference standards. This matters for quantitative accuracy.
3. Chromatogram: The actual HPLC chromatogram should be included or available on request. Look for a clean, single major peak with baseline resolution from any impurity peaks.
4. Endotoxin (LAL) test: Should show <0.25 EU/mg for injectable peptides. This is separate from purity and relates to bacterial contamination during manufacturing.

If a vendor can't or won't provide the actual chromatogram from their third-party test, that's a yellow flag. Janoshik includes chromatograms in all their reports — ask to see it.

— this is the kind of expert input I was hoping for. The peptide content testing point from is also crucial. Let me share a real example:

I tested a vendor's "10mg semaglutide" vial. Janoshik results:

• HPLC purity: 98.4% — looks great, right?
• Net peptide content: 6.8mg

So yes, the semaglutide was 98.4% pure — but there was only 6.8mg of it in a vial labeled as 10mg. That's a 32% shortfall in actual drug content. At my dose of 0.5mg/week, that's the difference between 20 weeks and 13.6 weeks of supply.

This is why I specifically request the quantitative content test from Janoshik (they call it "content by UV" on their order form). It costs an extra $20-30 but tells you EXACTLY how much peptide is in the vial.

This is incredibly overwhelming for someone just starting out. I don't have the budget to test every vial — Janoshik testing at $80-100 per test adds up fast.

What's the minimum I should do as a new buyer?