tcsoftware - 8:47 am on Mar 29, 2012 (gmt 0)
Perhaps for pontifex it might be a good idea to redirect the merchant links off to subdomains to limit the impact of what they are doing.
Overall though Google shouldn't be handing out punishments for an unnatural backlink profile, only ignoring the links. The negative affect on your page rank would of course depend on the proportion of unnatural links.
If it was the case that backlinks could have a negative affect on your site then it would be very easy to destroy your competition and anyone buying a domain would run the risk of buying a 'damaged' domain.