I'm on girlsdateforfree and state on my profle that I don't want any married men or those in a relationship to reply because they're wasting my, and their, time. I also stipulated I wouldn't reply if they didn't post a picture (married guys shy away from this form of detection) so that eliminated most of them. If you fancy a guy and get to chat to them ask for their home phone number - if they don't give it to you (without a reasonable excuse) then you can assume they're hiding something.
On a positive note - I had no problems at all with married men, oh sure there's a few who slip through the net, but you should always go with your gut instinct. I've met some really nice guys from there and have had some fab dates. I'm fussy and don't settle for second best, they seem to like the challenge!
Go for it, everyone on there is wanting to 'date' someone special - unlike faceparty - and the guys have to pay to join so that eliminates any who can't afford to take you out and buy you a cocktail or two - lol!
Good luck, come back and tell us how you get on.