Rule No. 1, Get a pre-purchase aircraft and logbook inspection from an independant engineer who is not familiar with the aircraft.
Rule No. 2, If the engineer says "Don't Buy It" then Dont Buy It.
Rule No. 3, work out how much it will cost you, and then double that.
Rule No. 4, If you don't like that answer then you can't afford an aeroplane.
Harsh and cynical but true!