I would feel good about buying any timeshare weeks including high dollar resorts at Wyndham, Marriott, DVC, or HGVC from the high volume e-bay sellers with a proven track record. I would be more wary of buying a week from an unknown individual on the numerous web sites that allow anyone to list anything with no verification of who they are. On e-bay you can read feedback from many previous customers giving yourself some confidence that they are legitimate. From an individual on redweek or myresortnetwork, you have to put more blind faith in the ad than you do on e-bay in my opinion. I can log on right now place an ad on Redweek for a Platinum Marriott Aruba Surf Club 2 bed room 2 bath that I don't own using a fake name, phone number and address. Marriott will not tell you who the owner of the week I list is because of the privacy laws. I simply buy a throw away cell phone to answer your calls and have my mail forwarded from a previous address to my new P O Box. There is no record of my previous sales to research or any previous customer's feedback on whether my weeks for sale were as advertised. Of course a person on those sites can be checked out through due diligence, but there is no Better Business Bureau to file a complaint with or any system in place to leave positive or negative feedback if they are con men and rip you off. At least on e-bay you can warn others if you have a bad experience dealing with a seller, and every time he tries to sell something your feedback can be read by all.
The only reason I don't buy the high dollar weeks on e-bay is because you win the bid, pay the money to the closing company, and 30 to 90 days later you find out the resort stold the week from you by using ROFR. Why go to the trouble and tie up your money for a week you will probably never own. Rarely does an e-bay bid get high enough to stop the resort from ROFR'ing it (although with the high air fares I feel that many resorts will stop most of their ROFR'ing when they get loaded up with inventory and sales slow down). I would gladly buy those weeks on e-bay if the resort had to actually outbid me to buy the week.
If your sale passes ROFR you know that you just paid more than the developer felt the week was worth, so they let you buy it. The purpose of buying resale is to get weeks as cheaply as possible. If the developer uses their "right" to ROFR, you know you won the auction at a good price, but the developer says for that price we want the week, so you still don't own it. I actually don't bid or make offers on any resort that has ROFR on e-bay or not, but if I was going to try and buy one of those weeks which have ROFR, I would still use e-bay to get it as cheap as I can and hope the resort has enough inventory to let my sale go through.
There is risk to buying a week from anyone including the developer (sometimes the salesman promises things that you don't get), but the huge savings over any other web site makes buying on e-bay worth the risk to me. Do your homework on the ad and seller, use a licensed bonded closing company, and enjoy the thousands of dollars you saved by buying on e-bay.