International vendor directory — need advice

Answering the narrow version, because the broad one does not have a single answer. Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion. Synthesis, testing, and cold-chain shipping have floors. A price well under the floor means something was skipped, and the two things that get skipped are testing and content.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

DataDave said:

Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.

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

traveltech_sara 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.

From the other side of the consultation, briefly.

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

Held at customs for 5 days, then released.

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.