You might think of using comments as one way to determine the authenticity of a blog. I have 3 blogs and one traditional site. 2 of the blogs accept comments (one is a deals site and it's not necessary or helpful to have comments) and while it couldn't be your only blog 'rule' it would be a good one to add to the mix. Rarely do the spam blogs receive (or even accept) them.

You might also think of memeorandum and their whitelist. They picked several hundred blogs to start with and then only included the blogs they linked to. There is a more inclusive process now, but at first it was almost invite only as far as what they considered blogs. Not sure exactly what their technique is now, just know they HAVE expanded past the original whitelist. check them out I think it's memeorandum.com

Even splogs accept comments also, difficult to use it as a criteria.

But the idea of white list is good, there is many services that could be used lik familyfriendlysites.com also. But its not a rule, cause not everybody could be affiliated.