The acting in catfish is so realistic, that it's borderline retarded that some people think it's fake: it isn't acting. The actors are so good at portraying emotions that it is almost undoubtedly real. But, of you suggest that it is really that's just as much of a hunch as saying that it's not.
I think "catfishing" is very real. Why not pretend to be someone else in a world where no one knows you or can physically see you? It is very easy to fool someone these days using the Internet. People get to be whoever they want to be. They lie and hurt real people who are looking for real things out there.
The action of "Catfishing" is definitely real because I have personally had a relationship with someone online who wasn't who they said they were. The MTV show 'Catfish' may stretch the truth and only use people who they already know are being duped. The show may not use the entire truth, but it gives people a chance to fix their broken relationship or give hope to their real ones.
The internet is full of bottom-feeders. Naturally any place that allows people to hide in anonymity will give rise to those who seek out ways to practice their particular disturbing behaviors. There are countless examples of people pretending to be persons other than themselves that you have to agree that the phenomenon is real.
The movie may have been inspired by a true story, but editing and scripting have clearly played a role in the finished product of the film. The TV show, however, is very much fake. Several journalists and investigators have released stories about how fake the show is and how the producers manipulate regular people into being on the show.