I've had my 99 rfi for a couple months now and its been pretty good so far. 150 compression is good. Water test needs to be done like others have said. It will have a 787 engine in it, not a 947. It should do 7K rpm and ~50-55 mph.
RFI's have a problem with the regulators/rectifiers, I'm not sure if they fixed it in later years. Might be good to take voltage multimeter and check voltage at battery when running. Should read between 13-14 volts. If its 15v or above its bad.
Also, see what kind of maintanance has been done on it. Stuff like changing oil injection lines, checking impeller clearance, filling impeller cone with oil, etc.
$3000 seems a little high, i'd try to talk him down a little. KBB is 2990 for suggested retail value without trailer. Used single trailers runs around 200-400. However, I'd remind the buyer that that price is from a dealer, who will normally with go through the craft and inpect alot more than a normal person.