Something that nobody has mentioned:

When you are trading emails back and forth (or you can find out his handle) - google search it.

I had a guy trying to sell a "perfect,no issues whatsoever" boat on another forum's classifed section. I did a search and found a number of posts from the owner complaining of problems and issues from years past.

I even noticed a boat for sale on this forum and did a search on all his posts - saw where his interior was in pretty bad shape back about 2 years ago but in the for sale post he mentioned where he replaced the seats. Trust but verify!