Because you can’t do I diagnosis of the problem and know that it is the only thing wrong with the car unless you test it. I don’t think it was dumb on the buyers’ part. Someone who is selling a car without even getting it looked at is likely to be a motivated seller who might care more about just getting it off their hands than they do getting top dollar. Maybe they developed a good rapport with the buyer and didn’t mind cutting them a deal. Maybe the buyer didn’t really mind missing out on the deal and wanted to be transparent. It is so funny to me the assumption that every person operates purely by wanting to manipulate the other party into giving up every last dollar in a business transaction when that is not how things work in the real world.