When it comes time to purchase an airplane, whether new or used, it's very important to do your own due diligence. It's good to trust others about what they have to say about the plane and it's history, but it's far better to validate that information on your own.
No airplane is perfect, especially a used one. If you're in the market for a "perfect" used airplane, then you're going to be looking a long, long time. All used aircraft will have imperfections; either with the cosmetics, older avionics, possible damage history, vague log entries, etc., etc. And most will have had instances in their history that will bear a deeper look. For example:
- Why does one cylinder continue to have compression problems?
- A major alteration was done but there is no FAA Form 337 to be found.
- Does the new interior have the proper flame retardant certification?
Cast a skeptical eye on anything that seems out of the ordinary. Make phone calls and ask for work orders or a more detailed description of the maintenance performed if necessary. Listen to your mechanic but get a second opinion. Most of the time there will be a sensible explanation. Sometimes not. And just because a major shop (or one with a well-known reputation) did the work don't always assume it was done correctly. People are human and mistakes are made.
Good luck in your search!