I imagine most people who "fake it" do so out of fear and desperation. They either don't feel that they aren't attractive by mainstream gay standards, have been rejected, etc, or they're deep in the closet. Whatever the reason, I think fear is the primary motivator.
I'm not sure that there's any reliable way to weed out the fakes. I've found that most fakes weed themselves out. It can be a bit frustrating, but I think it's a good example of why we shouldn't take the online world too seriously. Maybe you'll meet a good guy this way. Most likely, however, you'll have some interesting chats with guys thousands of miles away that go nowhere beyond this.
The way I handle "meeting" people online is to simply not invest too much energy into it. I enjoy a good chat and if there's a seemingly real connection, it will develop. However, I think there's a tendancy to invest too much emotionally into online relationships. We see some handsome pics, have a good chat, and before we know it, we're projecting all of our hopes and dreams onto the fantasy guy 2,000 miles away. That's the danger of online meeting, in my mind. It can set one up for disappointment.
I say enjoy your chats and let the fakes weed themselves out. After all, you might meet a great guy in a bar, go on a few dates, and find out that he's a total fake too. However you meet someone, you still have to do the detective work. ;-)