One of my hanger mates bought a nice looking c-150 and sent it off for an annual and rebuild at another airport. At the next annual the A&P said the compressions were way low. The owner said "can't be, I just had the engine rebuilt last year". The mechanic did a thorough check of the log books - engine number did not match engine number in log books, although it was painted up real nice. No proof that the switch took place during the previous annual or when? Ended up selling the plane at a loss to a mechanic that could deal with a run-out engine thad did not belong to the plane.
