There are good links and then there are some not good links. Some people call these bad links a "poison link" and many other negative nicknames.
When you are looking through a backlink profile, how do you prefer to define a bad or poisonous link?
Run of Site
Links that are placed throughout an entire website with identical anchor text could cause you trouble but then again I wouldn't refuse a run of site on Google.com
Do you want to use toolbar pagerank to determine if a link is poisonous. Having a toolbar pagerank of 0 is probably going to scare away some people.
If you are serving just the USA market, it can look weird to see Russian, Chinese and a bunch of weird international sites linking to you.
Google does say that you should nofollow links that you do not trust, so having people link to using a nofollow tag could say to Google your site isn't trustworthy.
How do you define poison links aka the links you would rather not have