Anyone reading this thread, just do your research, simple. Never had any issues amongst many purchases. Most markets are very similar to the the likes of Amazon, eBay, etc. Just look for sellers that have a large amount of orders (on verified & known markets) and have a decent amount of positive reviews alongside their order counts. You can also use the dark web's version of Reddit (Dread) and see what people are saying about markets, certain vendors, their experiences, etc.
Regarding the fake Xanax comment OP made, although they've now said they believe the Xanax they purchased to be legit. I'd recommend buying pharmacy grade blister packs, rather than pressed bars (not sure if they got loose pharmacy pills or bars tbh) unless you 100% know the source is legit. You never know what is inside pressed bars or the actual dosage unless you send them off for testing. Blister packs can be faked also, but if you find a legitimate source for them, they're gonna be dosed correctly with pure Alprazolam and will do the job right.