Is isn't true - RCI doesn't permit rental of exchanges or extra vacations - it violates your membership.
Legitimate businesses charge a commission after the service, but these companies all ask for a large upfront payment - they have no intention of ever renting anything.
Here are some warnings signs with these kinds of companies:
1) Did you get an unsolicited sales call or mailing or email from them?
2) Do they say that they already have a renter/buyer for your timeshare? (Or an established market like people attending conventions.)
3) Do they claim that they can get your money back from another scammer?
4) Do they want you to pay hundreds/thousands of dollars for a title search, or transfer fees, or taxes, or a closing fee, or appraisal, or ANY large fee, UPFRONT?
5) Are they offering to rent/sell it for far more than the market value?
6) Do they want you to pay a large up front fee that supposedly you will get back?
7) Do they want your credit card number over the phone?
If you answer yes to any of these questions, then this is the usual scenario:
Once you pay the fee and receive the contract, you discover that the company has only promised to advertise your resort, not to rent/sell it, and they don't mention having a renter/buyer in the contract.
Then, you won't hear anything from them for a long time, and when you contact them, they will tell you that the renter/buyer backed out, but they will advertise your timeshare on their over-priced website.
Finally, when you try to get your money back, they will point out that you signed a contract, and it's only for advertising.
When you try to challenge it with your credit card company, they will tell you that you only had 60 days to dispute the charge, and that it's too late to do anything.
This is a bitter pill to swallow, but right now, most timeshares are selling for 0-20% of the original retail price. It's not a good time to sell a timeshare.
To see what your timeshare is really worth on the current resale market:
1) Register with ebay
2) Sign in
3) Search for your resort by exact name
4) From the menu on the left click "completed listings"
5) The next page will show you current selling prices
(Be sure you look at the completed listings - those are actually SELLING prices - you will find asking prices all over the place, but what really counts is what they actually sold for.)