Darknet works like Amazon, but unlike Amazon reviews are usually real. Bad actors get blamed.
If they do, and there is a known risk, why did nobody in the distribution chain use a $15 test kit to verify the quality? Someone must have bought a few hundred pills at once to redistribute them, $15 and 5 minutes wouldn't matter.
Or general save drug use. You have a pill you haven't tried yet. No way to check properly. So you only take a bit and see if it turns out as expected.
This fentanyl thing is new and wasn't a thing when I popped pills. However there have always been dangerous pills. We've checked them, online, at labs, in person and small doses. If they were shit we throw them.
I believe the main difference is culture. We were aware of the dangers, we had mobile labs at parties and flyers about the current bad pills.
(Other than that Xanax and prescription drugs are nowhere as popular in Europe than they appear in the US)
Also worth noting in my state possessing kits design for testing for illegal drugs is a felony. [note: not legal advice]. No one reputable is going to risk a felony to sell drug testing kits for shitty margins.
https://www.azleg.gov/viewDocument/?docName=http://www.azleg...
https://dancesafe.org/drug-checking/
That said, how many users actually test every single drug they purchase? Especially if they are addicted and using multiple times per day?