In Germany government financed NGOs like "Verbraucherschutzzentrale" sometimes help to sue online dating sites.
This problem is referred to as "catfishing" in pop-culture and has been made famous by a popular MTV program called "Catfish the TV show".
Also, this model generally allows users to switch between free and paying status at will and without having to do anything, simply providing advanced features for a set period of time whenever the according payment is received.
Ease of payment is also generally higher, with such sites accepting a variety of online currencies, letting users charge the payment to their cellular phones, etc.
Such sites earn revenue from a mix of advertising and sale of additional options.