If you do your homework and know what price the seller should be asking then you can negotiate a little easier. If you know he's overpriced, make him a fair offer, if it's refused, walk away. Call him back in a month and if he still has it, offer your price again. This time he might be more realistic in his selling price.
Keep looking. Good RVs and prices are out there but it's not an easy job. Also, it's a plus if the owner has all the original paperwork and maintenance/repair receipts. He should also have the RV clean and presentable, not garbage and trash laying around. This is a conscientious seller.