There's really no way to tell if someone's a freeloader or not. AFAIK the 'allow freeloaders' setting within options doesn't work well, if at all. Browsing the host's not much of a guide either because the browse host feature's pretty unreliable.

Some people are true freeloaders, some aren't aware that they're not sharing & some might not be able to share (ISP limiting uploads, behind a stubborn firewall etc).