Freeloaders - how do I keep them out?

I have my option set to 1,000 shared files (just increased from 500), but people who offer no files to share still keep getting in ... "rarely" seems to be treated as "always", instead. I would prefer "rarely" to be equated to "never"! Especially when the freeloaders are accessing the rarest files available, because anyone wanting these should have similar rarities that I am searching for, for my own use.