I disagree with Alan Elbert, I ran 5 sites within the same niche (forex) which is silly competitive and we ran allow them on separate c class ISP to help cloak all of our linking and versatility on the web, not to mention soliciting each site as a stand alone company giving you higher revenue capabilities on affiliate partnerships etc

David, I have exactly the same issue with a few clients myself and what I have found is, if the client is a business that caters to just one specific area vs a larger span then the click throughs will vary and the customer reviews with close proximity of location tend to do best.

You might run into stubborn webmasters that just don't reply or tell you to fly a kite - so I came up with something that seems to work like a charm.

I inform them in less than 3 sentences that your site has been taking over by a trojan/virus/something scary and that it seems to be attaching itself to any and all sites that are linking to "me" so tell them for the safety of their site and any google penalization please remove the link and actually ask them to "let you know"

A great call to action and has been working for me

-Chenzo