Birds flyin' high...

It's often said that birds of the same feather flock together. For the most part, I believe this saying while keeping in mind that there is an exception to every rule.
so, when scoping an "object of attraction" and I happen to know his friends better than I know him I believe that I can make some assumptions about this person. If his friends are up standing citizens, good for him because I'm going to go off the assumption that he ain't quite bad a person. Of course, I'll still thread cautiously...but I can safely say that he has a pretty good head start.
If a guy, on the other hand, has friends that I don't respect...yikes! It's going to take a little bit to even grant him audience, talk less of anything else. In the case that I do look past his poor choice of friends (in my opinion) and decide that I should at least see what he's about, the following question comes up:

What happens if we do decide to get into a relationship? If I find myself REALLY liking this guy, but I ABSOLUTELY do not see myself being able to get along with his friends(not for the lack of trying), what do I do?

Is it fair to stay away from a guy/girl just because of the friends (close friends) they keep?

[Title taken from song: "Feeling Good" by Nina Simone]