In that listing you included the text "http://chipster.net/guide/guide.htm " but it is not "clickable" because it is just text. You have to use HTML to make it work so that it can be clicked on to go to the referenced site - you'll have to look at eBay's site to find out how to do that. My guess is that they want to control all links that point to outside location to make sure you aren't sending folks to a site where you might sell something without them getting their cut.