The only bad thing about those shops is when you're short of cash and wanna sell something and they offer you $5 for a camcorder...
:-)
They usually ask for proof of ID and address so the drug dealers and burglars usually go to the 2nd-hand computer stores with laptops etc.
I've never seen an Amiga in a 2nd-hand shop or boot sale, their appearance is very tempting to most (particularly the A500/600/1200).
The best place to sell though is on eBay as it has the largest audience who can bid and fight for a deservedly 'worth-fighting-for' series of computers. Amibench is another place to pick up and sell a bargain.
Damnit, when was the last time an A4000t made itself visible...
:-)