I too have been getting lots of non-Diser FB requests lately. I have been amazed at how many DISer's accept them as friends blindly just from their request and the number of friends in common. After a few issues early on - I began to ask what their DIS name is, if they didn't provide it. I have always included my DIS name with my request to other DISers - as they wouldn't know me otherwise.
I have my Privacy settings set to the most restrictive settings on everything. However, I do allow Friends of Friends to view photos of group activities, so that if I tag you in a picture your friends can share in what you been up to.
All accepted friend requests come with a "trial period" if you post Offensive posts, Fair Warning - I will delete you.
I am also selective about people I went to High School with and people from work and other aspects of my life. There was an incident here locally, where someone posted they were going to a concert and someone they knew 20 years ago in High School broke into their house while they were gone as they got the info from the post on Facebook where they were friends.