First of all, this rating is totally not important.It does not affect anything other than your perception. It is calculated from how many other members have this member in their friends or black list. The only thing you can get from it is if the member is popular with other members and/or behave mostly friendly or the member is not popular and/or does something that other people do not like.
Obviously, it changes over time. Some members change their opinion, some delete their accounts and their friends and black lists cease to exist.
Note, that number of people who have blacklisted the member has more weight than number of people who befriended the member. On average members have 10 times more people in their friends lists than in their black lists. Therefore the system gives more weight to the "blacklist" number.
Don't ask what you did wrong to get blacklisted. We don't know whats inside of people heads. And no, you can't see a list of members who blacklisted you. Unless you are a premium member.
Number of members who befriended Fritz: 199
Number of members who blacklisted Fritz: 9 (Why?)
Number of members whom Fritz has blacklisted: 6
Overall rating of Fritz is: sweet
(rating can be slightly out of sync with numbers, because it is calculated once per 24 hours)