hans_munich said:

Reconstitution tip for anyone mixing dosing arithmetic from lyophilized powder: use bacteriostatic water, NOT sterile water.

Right, and one flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.

Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

stefan_berlin said:

Quick syringe math for dosing arithmetic dosing: if your vial is reconstituted at 5mg/2mL, that's 2.5mg/mL.

There is a second half to this that has not been said yet. The useful checklist is about verifiability rather than presentation. Independent test results commissioned by buyers rather than by the seller, consistency across multiple batches over time rather than one flattering report, a physical address and a company registration that resolve, batch and lot numbers on the actual labelling, and a shipping practice that matches what the material needs. Everything a good-looking website provides is cheap to fake; none of the items above are.