Ach, they're not going to smash it up - but it is going to be very embarrassing.
Folk get conned on reps every day outside the forum - people often pay full price for a rep, we see folk flogging them on ebay all the time. So it's not surprising that they might take them to an AD. Frankly, offering to pay $400 to service it suggests quite strongly that you think it's real.
$400 is a big mark-up on a service - my guess is they will do a half-assed service, call it out, and keep the cash.
Maybe he should tell them that they tried to scam him by swapping the movement (joke!) Now that sounds like a case for Judge Judy....