Normally, a car dealer isn't going to let you take a car for a test drive without the sales person going with you, and you're going to need a driver's license to drive it. If I was selling my used boat, and a prospective buyer asked me to test it out on the river, I would agree if I went with him, and I'd want to make sure he was experienced before putting the oars in his hands. It may not be as easy and practical in some instances to take a used drift boat for a test ride as it to take a car, and I agree that a prospective buyer should not be offended if he isn't permitted by the seller to take the boat out to test, but it doesn't hurt to ask. This past summer I was looking for a new drift boat and had offers by a couple boat manufactures to take one of their used boats out for a day to see how I liked the model. Granted, this was at manufacturers, and not private sellers, but unless you are already familiar with the boat or that specific model, I think testing it out before buying is something a person should try to do.