I have a line on a used GK 700RB-II, which I've heard great things about. This one has seen very limited use. Are there any questions that I should definitely ask prior to buying this amp? I have contacted the seller and asked him if he is the original owner, how long he's owned it, if it ever incured any damage (dropped, liquid spilled on it, etc). I just want to make sure I'm covering my butt. Thanks for the help.