Online dating is risky, but not extremely implausible. People seem to use the day old excuse "But you don't know what they really look like!" however, modern times made that excuse outdated. There are video and voice chatting programs you can use to get to know said person better. That in itself shows you if they really match up to their supposed physical attractiveness. As for personality, that's easier to find out as well, don't focus on how they act around you or how they treat you. Focus on how they treat others, especially people who are strangers, or someone of a lower ranking (if you are on a forum). Their true personality will show through how they treat people "lesser" than them. Pay attention to the signs. If you have doubt, then get out.
Basically, use common sense when engaging in online relationships. And if you plan on meeting up, be in a public place and bring friends for safety.
The reason why people on Catfish get catfished is because they failed to use common sense. Like juankimari said, if they don't want to call you, or video chat with you, they are not who they say they are.