What terms did they offer you?
ANY company that charges a large upfront fee is not legit. They make their money with the upfront fee and then they make no attempt to sell/rent your timeshare.
Here are some warnings signs with these kinds of companies:
1) Do they say that they already have a renter/buyer for your timeshare? (or an established market like people attending conventions.)
2) Do they want you to pay hundreds/thousands of dollars for a title search and transfer fees, or taxes, or a closing fee, UPFRONT?
3) Are they offering to rent/sell it for far more than the market value?
4) Do they want you to pay a large up front fee that supposedly you will get back?
5) Do they want your credit card number before they send you a contract?
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.