Hmmm...
I'm probably going to get it. About eBay... It's not really a problem as affiliates or developers are allowed to use their web services like Amazon.
http://developer.ebay.com/
I was thinking for example, that a photography category could have a link that says something like "Search for photography items on Ebay." I'm not a programmer, but I have a similar thing in my directory where each category goes to a related Amazon category. I guess my programming partner could do it.