Answering the narrow version, because the broad one does not have a single answer. 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.

TrialTracker_MD said:

The useful checklist is about verifiability rather than presentation.

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.

chris_chi24 said:

One order arrived in nine days, one was held at the border for a fortnight, and one came back with a seizure notice.

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

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

International shipping tracking for cross-border ordering orders: my experience with customs in the US when ordering from overseas:

Package cleared customs in 2 days, no issues.

Tips: always include a copy of your prescription, declare medication properly on customs forms, keep quantities reasonable (personal use = 3 month supply max), and use a vendor who has experience shipping to your country.