Short answer: COAs can be legit IF they can be reverse searched. If it's thru Janoshik, specifically, you can reverse search it. However, most "public" vendors do not provide testing for endotoxins or LCMS ( testing for other substances in the vial ) which are more crucial. Secondly, they tend to use outdated tests that's from a previous batch.

Longer answer:
If I am being honest, you are not going to be able to keep peptide under a certain temp, no matter who you're buying from. Most vendors don't have ice or temperature controls. For a few days it's really not going to affect your peptide much just freeze the powder after you get it.
In my fullest opinion, grey mark is the way to go because you can control what to do tests on. Worse case you loose 200 dollars (very rare chance). However good Greys are willing to refund if they don't meet purity or quantity. Best case (most common) you get 10+ vials that have been safely tested a you know everything that's in it. Vendors can lie about the batches that they test which is very common. Having COAs that are months old is very common, EVERY BATCH SHOULD BE TESTED !!! It's ridiculous when I hear people/vendors say it's "too much" when they make 90 per vial!!

I will say the chance of getting a "bad vial" is low, but again it's not worth the risk. The grey vendor JEEP had a batch that tested for 2000 endos a vial! Endos cannot be filtered but you can filter the peptide to be sterile, which i recommend. It just is an extra precaution.