I know we always joke about it, 'Crack Convertors' is my favourite, but doesn't anyone selling to them has to provide ID and proof of address and such like? I used to know a bloke who had a junk shop and plod were always on his case about keeping records of what he bought from whom.
I know that's not foolproof or anything but I'm pretty sure you can't just wander in and sell them a mobile phone or something without producing some docs.
Current Lash Up:
TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.