So, I noticed that the vendor "Mr. Super Mario" claimed that his product was 93% pure. Since the typical product that's been available in the US has been more like 10-20% methamphetamine, I thought this was interesting. He also claimed to be getting his product directly from Mexico. Of course, the Mexicans have been shipping cut-to-shit dope since last winter, so this intrigued me. Had they finally stopped screwing around and gotten serious? Mr. Super Mario had two certificates of analysis that claimed that, in fact, they had! I had a look at them, and they did seem to check out. Except for the minor issue that they were both dated March 2016. Well, no shit, everyone was selling good product in 2016! What about a certificate for the stuff being sold mid-2017? I'd sure like to see what one of those would say!
Even though his initials would suggest that his product is cut with methylsulfonylmethane, it's almost certainly actually cut with n-isopropylbenzylamine, since that's been the Mexican cartels' adulterant of choice.
If you think you got fake dope, or heavily cut dope, melt some in a tube in hot oil and measure the temperature with a glass thermometer. It should be all melted below 200C. Then take it off the heat and keep an eye on the temperature as it cools. Real meth will start to solidify between 170 and 175 degrees C, and will only change temperature a degree or two before it finishes solidifying. Heavily cut bullshit, on the other hand, will start to solidify at a lower temperature, and will change temperature A LOT while it's solidifying. This difference between how pure substances and mixtures solidify is what's responsible for "crackback" patterns.
edit: More info on how to do a melting point test and how it works
Unfortunately, pure bullshit will have good-looking crackback patterns and will test as a pure substance too, so it would be good to also test with the Marquis test. However, I have not verified any pure bullshit being sold on the darknet to date, although TheSaltonSea on Dream came pretty fucking close. It's all just been heavily cut with n-iso, at least the stuff that's coming out of Mexico.
Heisenberg?