Favorite supplier / where are people buying these days

COA is non-negotiable. Third-party COA specifically. Any vendor that runs their own 'internal' testing is not a serious vendor.

Third-party COA, recent batch, readable HPLC trace. Everything else is secondary. Fast shipping with no COA is nothing.

For me: reliable reship policy. Stuff happens in shipping. How they handle it tells you everything.

Customer service is underrated. When something goes wrong — and it will — you want a human who responds in 24hrs, not a chatbot that takes 3 business days.

COA + proper lyo (you can tell from photos if you know what to look for) + consistent batch quality over time. I don't switch vendors unless I have to.

Discreet packaging is actually on my list. I have a nosy mail person.

I rank them by: COA, then consistency, then price. Fast shipping is nice but I've gotten garbage from fast shippers and gold from slow ones.

Request multiple COAs from different batches. If they only have one they keep sending you, that's a flag.

Also: does the COA have identity testing (mass spec) or just purity? 'Purity 99%' of the wrong molecule is still zero useful to you.

^ this is the question nobody asks. Mass spec identity or don't bother.

For GLP-1s specifically: clean lyo, correct vial labeling, and no weird discoloration. I've had two vendors send me yellow-tinged tirz. Not running that.

People forget: a good vendor might have a bad batch. A bad vendor is consistently bad. Don't judge on one order.

Nice-to-have for me: international vs domestic. Domestic costs more but it's what I pay for when I actually need something fast.

Lurker here — this whole thread is the checklist I wish existed when I started. Thanks.

+1 to polite_guest. Saving this thread.

One more: how do they handle custody of the vial between manufacturer and customer? Reputable vendors answer this; shady ones get defensive.

OP — this is exactly the thread I needed, thanks everyone. Updated my checklist: 1) third-party COA with mass spec ID, 2) multi-batch transparency, 3) reship policy, 4) human CS, 5) discreet packaging. In that order.

Bookmarking this post as the only acceptable answer to the 'best vendor' question going forward.

Honestly all those checklists mean nothing if the guy running the op is cutting corners anyway. COAs can be faked, batch transparency is theater if he's just relabeling stock, and a "reship policy" just means he'll send you bunk stuff twice instead of once. The only real non-negotiable is if you know someone who's actually used them and didn't get ripped off, but even then that's just luck.