I wonder if it is OK to sell on eBay an information on how to get something cheap, etc. I would sell a simple ebook (actually just a short 100-words article) on how to get a certain product. The ebook would include my affiliate link (would be hidden) and the price of the ebook would be minimal - e.g. $1. Generally, it would be a good deal for the buyers and the chance that they click on the affiliate link and buy the product would be high I think, as they would even bid on my ebay auction to get the information.