I would suggest you consider
www.myresortnetwork.com or redweek.com or listing your timeshare on eBay. If you price it right, it should sell as Vail is a very nice location.
You have to be realistic, however. The economy is not good, and the timeshares that are selling are going for very low prices. I recently sold one of my timeshares on eBay...so it is possible...but you need to be careful not to overprice it. I'd start with an opening bid of $1 and have either no reserve or a very low reserve price.
It's my opinion that you should not pay a large upfront "advertising", "marketing", "appraisal" or any other kind of fee to someone who wants to help you sell your timeshare. Some of these may be legitimate companies, but it's questionable that they will be able to sell your timeshare for anywhere near enough to cover their fee and also provide you with some profit. Typically, these companies overprice the listings (basically telling the seller the property is worth what they want to hear) and then the timeshare doesn't sell.
Also, if someone calls or emails out of the blue and offers to buy your timeshare...and it sounds to good to be true...it almost certainly is fraudulent. There are a lot of scams going around. Don't fall for them.
One easy way to tell a scam is if the person is eager to buy your timeshare without asking any questions about it. Real people don't do that. They ask questions. Also, if an email contains broken English, that's a red flag. Finally, if someone wants to send you a cashier's check or wire for more than the amount of the timeshare and then have you refund the difference, that is a definite scam. Run the other way!
Hope this info. helps.
Steve