Here is the funny thing - some dancers get insulted if you DON'T have a boner - they'll keep checking - and they'll be very excited if you do have one - and will do everything they can think of to keep you hard as a rock and agreeing to more dances with them.
Other dancers that have had unpleasant experiences with guys coming in their pants, presenting the dancer with a rather gooey lap to be sitting in get a bit freaked out if you're really hard and will keep saying, "You're not gonna cum on me, are you?" or "When you're gonna cum, can you give me a warning?" I always tell them that I've never presented any dancers with such unpleasant surprises and that if I get close to that point, I'll yell out "Thar she blows!" or some such comment. Most dancers trust me after that. I have had an experience with one dancer, who I had a lot of fun with previously, that was so freaked out that I couldn't get a good dance from her. She retired shortly thereafter, mercifully.