This one has a reasonably settled answer, so here it is. 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.

HPLC_Greg said:

The useful checklist is about verifiability rather than presentation.

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

jason_sac26 said:

Living somewhere the domestic route does not exist, which makes most of the advice on this board inapplicable to me.

Agreed, with a caveat about community reputation: it is a lagging indicator. Reports arrive weeks after orders, so a supplier can look excellent for a month after quality has already changed.

Adding the clinical framing, because it changes how the question reads.

My experience ordering cross-border ordering internationally: I've ordered from a Canadian pharmacy. Customs can be hit or miss.

Shipping time: 10-21 days
Customs clearance: held for 3 days then released
Quality: Janoshik tested at 98.2% purity

International ordering adds complexity but can save 60-80% compared to US prices. Research your country's import laws first.