Clinical perspective, offered as context rather than as advice. There is a difference between no evidence and evidence of no effect, and this subject is one where the two get swapped freely in both directions.

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

From the other side of the consultation, briefly. If two explanations both fit, the useful question is which one predicts something the other does not. That is answerable; arguing about which sounds more plausible is not.

claudia_zurich said:

If two explanations both fit, the useful question is which one predicts something the other does not.

This is my experience too, for whatever a second data point is worth. Posting only so the count is not one.

claudia_zurich said:

If two explanations both fit, the useful question is which one predicts something the other does not.

There is a second half to this that has not been said yet. The pattern that distinguishes a bad batch from an exit is behaviour rather than product. A bad batch comes with communication, a reshipment offer and a batch number. An exit comes with slower replies, pressure toward less reversible payment methods, sudden discounting, and the same reassurance repeated without any new information. The product tells you less than the correspondence does.

Moderator note: good thread. Keeping it here rather than moving it, because the question is general enough to be useful.