I'd imagine the odds of your post getting checked is pretty much zero to be honest, I mean you'd get a baggie in a standard envelope no problem, and thousands of them go through the sorting office every day.

I doubt I'll ever figure out how to access the 'deep web' or whatever, let alone actually purchase anything,but thought it'd make for an interesting thread to hear people's experiences. It can't be that easy to just order some black tar as if you're on ebay or whatever, surely?