the man was able to tell. He asked me afterward and I had to come clean. Ever since then I always feel too guilty to even attempt to fake it. I know for a fact that I'm very expressive with my face so if I'm not climaxing, my face gives me away. I have a very distinct "O" face that I just can't fake.
I thought it was over, but he actually appreciated my honesty, and tried even harder to help me get off. A lot of men genuinely enjoy pleasing women to completion, and faking it doesn't give them any idea of what they may or may not be doing right.
And to piggyback on the OPs statement, just because I didn't get off doesn't mean I didn't enjoy myself. It takes anywhere from 15-25 minutes to get me off anyway.
I had a friend who always faked it, needless to say, after a while the volume of clients decreased. Could be that she was a horrible actress, who knows.