I assume you're talking actual ownership. If so, it's really just two sales with reciprocating buyers/sellers. I did a "swap" of a timeshare for 50 OKW points a few years ago, win/win for both of us. I've looked at many other potential scenarios over the years including members of this BBS. The problems are many but include finding two people that have what the other wants and even when you do that, coming up with a price for each acceptable to both parties. As a rule, one party wants to hold the other up by either over valuing or under valuing one component or the other. Best to just sell what you have and buy the one you want in most cases.
Also, in the timeshare world there is a rash of companies that will allow you to "trade in" your existing timeshare. However they ultimately don't get it changed to their name and you end up owing the fees for something you thought you no longer owned.
You didn't mention what you have, but if you want one approximation of what it's worth, go to eBay and do a search for your timeshare company. Then click on "Completed Listings" on the lower left side of the page -- that will give you the actual sales and uncompleted sales.
You may be shocked. A lot of other timeshare products from very good companies are selling for pennies on the dollar. And there are also a lot of completed auctions with $1 minimum bid that got zero bids.