Craigslist transaction went south...

the primary red flag on this deal is the guy immediately threatened you with legal action.   Over a $120 sale.   I would have to assume right from the start that something is amiss.     Either he lives under a rock and has no clue that situations such as these require tact in order to resolve with minimal stress.    Or ,  he is scamming you.  If you can not be sure that the unit he presents to you is not the one he sold you then tell him that and wish him luck.    Meet him in a public place to ascertain if it is the same unit.  There must be some identifying mark on it that you would remember?      This is of course a lot of hassle like many have said on here...but do you really want to give money back for a unit that is broke and not yours?     It is indeed the principle factor in play here.   You might want to just confront him with your suspicions and see how he responds.    Again,  what sets this all up as a scam is the guy making a threat on the initial contact of something wrong with the unit.    Maybe he is a bit of a doofus and knows squat about electronics  and thinks this is what he needs to do to get it resolved.   Poor communication skills if thats the case. 

meant to say if you can not be sure that the unit  he shows you is the one you sold him then I would walk on it.