LibrarianMeg said:

It helps to ask what evidence would change your mind before you look at any.

Same pattern here, and in the same order.

quinn_sf said:

One practical note: write down what you did and when, before you need it.

Coming at quinn_sf’s question from a different direction. The distinction that resolves most of these threads is between what is true on average and what is true for one person. Both are real; they answer different questions and get quoted as if they were the same one.

Adding the numbers, since they settle part of this. The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the same conditions. Nobody wants that answer and it is still the answer.

Following on from quinn_sf — and this may be the naive question:

How long did you give it before you decided it was working?

Moderator note: the sourcing question belongs in the vendor section and has been split out.