Well, I have not sold any points, but I would assume there would be broker fees like in any real estate transaction. Closing costs are negotiable between the buyer and seller, as are the current dues.
Do NOT work with a broker that wants a fee upfront to accept the listing.
In fact, I would not hesitate to contact The Timeshare Store, our board sponsor, and ask them what costs are normally the responsibility of the seller on DVC resales. Tell them how many points you want to sell, and the contract deltails (all one contract, add-ons, multiple contracts) and they should be able to give you a ballpark guestimate.