Clinical perspective, offered as context rather than as advice. Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then measure again under the same conditions.

sophie_paris said:

Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then…

This is my experience too, for whatever a second data point is worth. I had assumed I was the exception until I read this.

sophie_paris said:

Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then…

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.

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

One concrete data point for the thread. Keep the original post as written when you update it, and add the correction underneath. An edited-away mistake is invisible to the next person who makes it.

One thing that is still open after sophie_paris’s answer:

What a vetting checklist should actually contain, as opposed to a list of things that are easy to fake?