Another thing that I do is not to let prospective buyers fly the plane unless there is money in hand. My brother learned the hard way by giving away unlimited free flights. He even flew long distances for demo flights. No more.
If someone is serious they will not need to fly it. A tire kicker will use the guise of a purchase to get a free flight out of you. Everyone should know how a 150 flies.
In my experience serious buyers look at the logbooks and get all they need from that.
Jim