You can use links on your 'about ME' page, but they're getting a little strict about those too. As far as I know that's the only safe place to use a link. If the links reference selling on another site (your own website for example) they will remove it. Here's Ebay's link from their help pages, telling you what you can & cannot use:
http://cgi6.ebay.com/ws/eBayISAPI.dll?MfcISAPICommand=S...1&searchString=links
BTW Auctiva links are ok