I believe they charge an upfront fee - something in the neighborhood of $599. That's a no-no at TUG. And forget about any money-back guarantee.
For more info about upfront fees and some practical advice on how to sell your timeshare without getting scammed, read the "how to sell" article at the top of the list of topics for this Buying, Selling, Renting forum.
Also at the top of the list of topics is a list of resellers that TUGgers have successfully used.