As you said it doesn't have his real name so not sure why he would not be a little more vocal about getting someone to buy his eBay. It would be hard for Wyndham to track who he really is based on this forum.
Actually this is not true. Be careful what information you provide here if you don't want to be identified. All it takes is a customer database, a couple of facts about someone (going back through their posts), and someone who can write a decent query and you can find out who an individual is. It takes very little information to uniquely identify someone with all the data available these days. Zip code and date of birth are all it takes to uniquely identify most people in the US. Wyndham could use any combination of information about a member's dates/locations of stays, references of calls to owner service, number of points, residence location, number of contracts, home resorts, etc and narrow it down to someone very quickly. It wouldn't even have to be exact information, especially if they have multiple pieces to draw upon.
And if Wyndham already buys data for marketing purposes (which they do) and link that to their customers it's all over, because then they know your income range, occupation, as well as many other personal details about your household, spending habits, and can use that information along with your posts to identify you. The marketing companies basically know everything about you unless you and your parents were extremely careful to the point of living off the grid.
Grocery stores and credit card companies sell a lot of information to marketing companies who then sell it to companies like Wyndham. And no, your insurance company didn't violate HIPAA and tell someone about your diabetes, asthma, preganancy, etc. That was Target, Walmart, or your grocery store using your other purchases to figure this out and sell it to someone. Assuming that your free email service from yahoo, microsoft, or google didn't sell the information they pulled from your emails first.