What is the proper etiquette for responding to inquiries on Yahoo Personals?

I recently added my profile to Yahoo Personals. I've been getting lots and lots of responses from interested guys - they all seem very nice, but none are the right fit. I'm not a paid member, so I can only send icebreakers at this point. I've been ignoring them up to this point, but I don't want to seem rude or anything. One guy even sent me two messages telling me of his interest. How do I respond as politely as possible? I just want to say "Thanks, but no thanks".