Most are scams
I'm not proud to say I've signed up for a few dating sites in the past and the experience has been variable to say the least. Most sites will not let you post messages until you've paid cash
My method for signing up to a site is to just post a basic profile with no picture and wait for a week. If I'm inundated with posts from profiles of hot woman twenty years my junior desperate to hear from me and urging me to message them back then I unsubscribe immediately. There are too many sites that employ ringers whose sole purpose is tog et you to sign up in the vain hope that they are actually a) real and b) interested in you.
As soon as you part with the cash and sign up, you never hear from them again and the messages almost immediately stop and they are notoriously difficult to unsubscribe as well (have to phone up a premium rate number between the hours of 7am and 7.30am every alternate Wednesday on a leap year).