I think a lot of fetish sites in general have at least a few people that pose as the opposite sex. I've encountered it on various places and, while it generally is men pretending to be women, I have encountered the opposite scenario where women pose as men. I believe it all boils down to the freedom that comes with pseudo anonymity. Life becomes mundane at the best of times and maybe people just want to experience the thrill of being someone they aren't, or perhaps some do have more nefarious reasoning, but when I've encountered it it's mostly people that are simply bored and truly mean no harm. I'm a bit of a nerd so I've encountered women posing as men, but they do so more or less to provide a sort of barrier of protection from harassment. Women get more attention and if you just want to go about your business, pretending to be a guy shakes off a lot of unwanted interactions.
I did encounter a man pretending to be a woman on another BDSM site not long ago and it honestly hurt quite a bit because I had exchanged with them several times and started to feel something. I suppose guilt got to them and they revealed that they were a middle aged, married man and posed as a lesbian in order to "not cheat". They explained that they felt if they weren't being them then it was just all pretend and didn't count. It wasn't the first time I've come across that reasoning. I ended the conversations and they didn't understand that I wasn't ending it because they were male (I'm more or less pansexual, but I do lean towards being more attracted to men), but because I don't condone cheating and no amount of wordplay would excuse that they were indeed cheating in my opinion. I've also had "lesbians" confess that they were really just bored guys that were embarrassed that they didn't have a lot to offer and wanted to get some sort of online interaction and, as has been noted, women get more attention. Some of these guys would tell me that they're straight, but would message male accounts as women to get anything in response.
I haven't been dealing with online sites like this for very long but I have picked up on ways to tell for the most part if someone is masquerading. Then again, it doesn't bother me. I like being able to share interests with people and I could honestly care less about someone's sex or gender. (I apologize if my terminology is wrong. I really don't mean to offend anyone. I have the social skills of a drunken squirrel with rabies.) I do hope that people will be honest with me eventually and, again, I don't care. But that is because my philosophy on dating is simply, if the feelings are there, I don't care. I understand some people don't share that line of thinking and it is upsetting. I can relate to that as well because, again, I've fallen for women that didn't exist, men that didn't exist, and everything in between. It sucks because I just really want to find someone that doesn't think I'm too terribly weird (I have no social skills and I'm a biological female over 6ft tall so the deck is already stacked hard against me but I keep trying.) It does make me a bit discouraged when the rug is pulled out from under me, but that's life. Disappointment is just part of existence so I just try not to let it dissuade me.
I just feel like people should enjoy their interactions with people and, if things start to move to real life or feelings start to develop, ask for the cards to be on the table. Most people who are pretending move on after getting a fix and that's that. If you don't like the way the cards fall, just consider it a learning experience, or just an experience, and find someone else. Don't let it sour you on things. It seems there are a fair number of men and women into kink of all flavors so someone has to match eventually.