E.T.
Timeshares are sooooooooooooooo hard to sell. If you look at all of the companies that offer resale, the prices are super low because the inventory is so high and demand is low. Can you join RCI or another points type place and then bank your weeks until you find the time and desire to go somewhere? Or how about giving your week away to family or friends who might want to pay the exchange fee/annual cost in exchange for a "free" vacation?
And yes - as with most things, don't pay to sign up with a service that will sell your timeshare. There's no guarantee that they'll sell it, but there IS a guarantee you'll pay the fee. Do a little searching to see how much a similar timeshare goes for (same week/property if possible). - that will at least help you determine whether you'll save more by trying to sell, or whether it's worth it to default.