How can you tell if girls post on Craigslist Personals are for real and ads?

you can't tell but i did meet one girl on craiglist unfortunately she was a virgin and didn't want to do anything untill she gets married and wanted a rock on her ring asap. i think those women are not only selling themselves on craiglist but on all these other dating sites its hard to meet someone from these sites unless you can talk to them over the phone and they aren't selling you anything