I've just implemented wp-ebay-ads on one of my websites: http://www.quirkycars.net..
I've integrated it with Feedwordpress using the custom field options.
It's actually very simple: for each RSS feed in FWP, I set the ebay_search field to the required value.
Then, in the template, I have a section of php code that calls wp-ebay-ads, but ONLY if the custom field is set. And ONLY if it's NOT on the front page. (I.E. the equivalent of "single.php", which my theme doesn't have..)
So, I end-up with all my (ebay) rss feeds creating posts, which when clicked, bring up a list of related listings on ebay. Result!
The only time-consuming part of this was adding the custom field settings in FWP.
It's now up and running, and entirely automatic.
I'll be keeping an eye on the stats from today onwards..
** To see how it looks, just click on one of the newer posts on the frontpage - the older posts do not have custom fields set..**