Planet13 - 10:13 pm on Aug 23, 2013 (gmt 0)
Definitely check if they are nofollow or whether they could flow page rank.
But if they do flow page rank, that would probably be a prim candidate for the types of links that google WANTS to devalue / punish.
Another is that if the site in question is spamming then it's possible that they have links from a network of sites designed to boost rankings, and that link discovery bots are banned from the network to confuse other SEOs.
In that case, the only way to find those links would be to use google, I think.