1st off, don't ask if he install the switch for u...Just tell him u got a Live account and u need to know how to disable/switch off the modchip...(Being that it's a chip in there that he was supposed to install, he should be able to tell u quickly how to disable it)...This is how u catch him...If he's cool, he'll say just bring it in, if not he'll give u the runaround, that's when u tell him ur gonna visit him and bust him up...
Nah don't bring the cops in it, not exactly a legal transaction that went on between you and him, considering u bought a hacked bios...I would leave that out....Just threaten to whip his ass, and if he doesn't budge, go whip his ass for real.
I would just call him, tell him i know for a fact he didn't install a mod, and he only did tsop, and that i don't want no money back from him (cuz ur not gonna get any anyway) I just want him to install a switch and flash half of the tsop with the stock ms bios it came with and the other half with the latest X2 bios...And be done with the whole thing...I know u feel played, but that's a life lesson and being the type of deal this is, not much u can do about it...If he just sold u a legal chip with cromwell on it or something, and it didn't work, then u would have a gripe.