eBay integration is described in the following thread: New feature - eBay integration! (Beta). The following is a summary from that thread:
You can connect eBay auctions to games on BGG. You can list any auctions you like - they do not have to be your own. You will get 0.01 geekgold for every auction you list (added when the auction ends), plus an additional 0.01 geekgold for every click that auction receives, to a maximum of 0.05 geekgold per auction.
Total geekgold earned by connecting eBay auctions may be viewed as follows: My Geek/Profile/Geek Stuff/[click on collected amount]/[check the area below your username]. Note that only a total (not a breakdown by auction) is available.
The auctions appear by default in the eBay Module on the front page and on each game page. If you have indicated on a game page that you want to be notified of sales for a game, you will now also be notified if a game is listed for auction on eBay.