To create a good impression on a potential buyer you need to prepare your race trailer so it's looking its best when the buyer arrives.
Consider having it detailed by a professional detailer. For a couple of hundred dollars you can have your race trailer cleaned from top to bottom.
If you opt to clean it yourself make sure you clean in all the hard to get at areas, like door openings, office, lockers.
Never leave anything lying around the interior or office making them look untidy in the eyes of the buyer.
Clean up any residue of polish after you're finished to avoid giving the impression you've just cleaned the racetrailer up to sell it.
Consider having the taillift oil changed a week or two before selling it so it looks nice and clean and the lift will work for demonstation. Doing it a week or two before will mean it won't look too fresh on the day.
Take the time to inflate the tyres to the correct pressure.
Have the racetrailers service record on hand to show the potential buyer that you have had the race trailer serviced regularly. It's another way of demonstrating you've looked after it.
Also have the race trailers title on hand to show that you are the owner of the race trailer you're selling.