I have sold everything from a 12ft tinny to a 45 foot cruiser. All I want is a fair price for me (the seller) and them the buyer.
I do not tolerate demanding or rude buyers, nor tyre kickers.
Water Testing a boat is way different to test driving a car. A car you can easy drive around a block. A boat you may need to travel some distance to a boat ramp, then after the test you need to wash boat and trailer flush the motor and then pack away - this all takes a whole lot more effort than a car.
All I request, is some commitment from the Buyer. If they are not happy to provide that commitment, I will also walk away from a sale as a seller.
There is always a genuine buyer out there when you sell at the right price.