On the small uncontrolled field where I did my tailwheel training, there was a neglected (certified) plane in the grass tie down area. It looked really bad. One day I came out, and it was up on blocks. Next day it was sitting on the same tires but they now had air in them. The owner spent a few days doing work on the plane. (Unknown if the owner was an A&P, but most likely not) The airport manager came by and I asked what was going on. The manager said that he had not seen the owner in almost 10 years.
Well the owner started it up and ran it hard for 20 min. A old time instructor walked up and asked his intentions. He was going to take off and transport the plane for sale. We could not convince the guy to have it looked at by an A&P. Whoever bought that plane better have it checked out.
All sorts of neglect can be covered with some armor-all and a rattle can of paint.
I still think of that plane every time I visit that field.
But, heck, maybe sitting in the Houston humidity and heat for 10 years had no effect on the plane and it was perfectly fine. Or maybe the mud dabbers protected it with their nests. Hey, it was certified so it must be safe.
In another story, a business acquaintance bought a beautiful, newly painted, certified plane. It was checked by the current owners A&P and the annual was signed off. Next annual and the new owners A&P found massive corrosion of the main spar. That was the end of that plane. It never flew again. But it took 5-years, and many inspections, for the new owner to come to terms with the situation before he sent the plane to the salvage yard.
I was lucky. I had essentially bought the plane sight unseen and had a mechanic (and an RV builder) check it out before handing over the check. But I was heavenly invested in the plane without knowing the condition. It turned out to be a great deal.