That's never happened to me, thank God, and also I've never done any cyber relationships, which is maybe what you're asking about. It's possible that someone once represented himself as having more experience than he did, and maybe wound up somewhat out of his comfort zone, but I think he was deceiving - if that's even the word - himself more than me. Look, a lot of these interactions are based on fantasy. You'd hardly spend a lot of time with someone who presented himself as unexperienced, selfish, ambivalent, and ignorant, would you? And lots of times people become what they pretend to be - for good or for ill.
So my advice, similar to others', would be to pay attention to signals, especially little ones. Is his information consistent? Are his rules similar to those that others outline here and on other sites? Does he know the difference between pushing limits and violating boundaries? As far as I'm concerned, no means no, especially at first. I've never used a safeword because I've never done the "don't, stop - don't stop" thing. (Not that I would mind, at a different stage in a relationship.) So I try to be as clear as possible in my signals and I want them respected. I think that even a little bit of inconsistent stories, or being pushed when it's not appropriate, would cause me to back out.
And that's the other thing. A lot of these interactions are based on fantasy, but if the other person is behaving poorly you need to be able to step back from the fantasy and recognize it. Before someone gets hurt.