Lets assume for a minute you like ZR-1 Corvettes built between 1990 and 1995 like I do. On the ZR-1 Net is a crowd of about 600+ members all over the world but mostly in the USA that own these pedigree of C4 Corvette. Collectively speaking many people know about certain cars, their owners, and the cars history and can learn in advance about a specific ZR-1 that interest them. This is just one niche in the world of performance cars... there are others.
If I go to someones place to look at a car or a motorcycle I check out everything that is easily visible. How and where somebody lives tells you a lot about how they take care the motor vehicles they own.
Buying at auction or at a dealership is where the mystery is the biggest... lease returns are usually pretty solid but not priced as well as private party cars on average.
People buy and sell cars and motorcycles for a multitude of reasons... it's not always because of problems.