This sounds like a perfect example of someone charging a LOT of money for something that you could do yourself and they are more concerned with getting that money than any results for a sale. It also sounds like they have themselves pretty well covered in case your unit does not sell. If you really want help selling your unit, put it on a consignment lot. Although they can gouge pretty deep (10%) at least they have a vested interest in selling it. They don't get paid if it doesn't and the more they sell for the more they make.
Lots of folks sell RV's themselves every day. Price it right and advertise for free on Craigslist. Sold my last MH that way. If it's not priced right, it won't matter how much effort you put into selling it. If it's priced to sell, it will.