Just bought a boat so that might qualify...
ASK QUESTIONS! Talk to the seller, email and phone if he'll give it to you. He should... if he doesn't look elsewhere. One of the biggest things is getting a feel for what the seller is like. By the time the auction closed, I didn't even have to send a deposit. We went and picked it up personally the following week. I brought a cashiers check with me. Inspected it, and then handed over the money. Many won't do this, but the better sellers are willing to work with you. This one turns out was great. There was a hidden problem with it, the seller is taking care of the bill to have the shop fix it. So I don't even have to spend my time doing it. He had also said if there were any problems, or I decided I didn't like it to let him know, and he'd buy it back from me. And that was after he had the check.