Ask for a service record, Inspect the interior for stains rips etc. Ordinarily an owner that takes good care of a cars interior also does regular mait. such as oil changes and other fluids. The visual appearance of a high mileage car is a window to the things you can not see.
Do you have acess to any pics to post up on the board here.
A lot can be said about the previous owner by how well maintained the car is.
If kbb says its worth 2600 in fair condition why is he willing to let it go for so much less?