WHY would you pay a company to buy timeshares for YOU off eBay?
Set up an ongoing search on eBay ... learn about sniping in the last few seconds ... check out eBay stores of the major re-sellers ... have them look for product which you really WANT before they put it up on the web.
So unless you want an impossible TS product ... for about free ... you can try to hunt down units/resorts/locations you are interested in.
I still truly recommend you visit (day visit or a short stay) before you BUY at any resort. If a points system, check out MORE than 2 resorts ... and spend LOTS of time talking to other owners before buying about easy of booking, fees to use, how units are assigned, booking windows for best outcomes, etc.