Is it possible to stop a site from showing your ad if they are using Yahoo/Overture backfill to power their search. Here is an example of a site that does this: http://www.gasta.com/ so if you perform a search and hover over one of the results you can see they are powered by Overture. Now this site converts dreadfully for me, like 0.6% when I normally expect to see 50%+ from Yahoo.co.uk I really want to stop sites like this sending me crap traffic. Is there any way I can do this?