I think most of the ads are, in fact, real. However, it is often difficult to tell from the ad whether it is one of the majority or the minority. That's where the Forum can help. Between experienced guys sharing tips to detect a potentially fraudulent ad and asking for feedback on a specific ad you can get help sorting the decent guys from the not-so-decent ones.
EDIT: I agree with @Tarte Gogo - tell us who you are interested in and someone will help. And welcome to the Forum.