welcome. cant help with the "which vendor" part, thats the no sourcing rule and it counts for me too.
but the checking part is more useful anyway. before you even look at a batch number, look at the shop. do they test at all, and do they keep doing it. how long have they been around. are there reviews, and are they from real accounts or new ones. did they claim their listing and put a name on it. none of that is proof. but a shop testing for two years is not the same as one with three COAs and a nice logo.
then the batch. ask for the report for your batch, not just any report. check the number on the paper matches the number on the vial when it comes. and see if the lab has a page where you type the report number and get the original. no page, no way to check, and then the PDF is all you have.
china direct, people test more, which is good. but people have reported vials from the same order coming back different. some fine, some not. so one test tells you about one vial, not the whole box.
which is the honest part really. you can make the odds much better. you cant make them zero.
what happened last time if you dont mind saying? paid and nothing came, or something came that was wrong? those are pretty different problems.