A developer complained on the eBay Developer’s forum about cookie stuffing using iframes. eBay’s response was they “have monitoring in place to capture suspicious behaviors and poor value traffic to help us quickly pin point questionable affiliate practices.” Here’s the link to the forum.
eBay affiliate links within eBay listings is prohibited in the Ts & Cs of the eBay Partner Network. However, you can see some people do add their affiliate links which are clearly visible in the listing description. Check out this search for “rover.eBay.com” on eBay.