You are so right, DNJ. I haven't played in any bars in quite a while. I do the supper club, but the owner will back up whatever I decide to do about guests. If it's someone I know is good, I'll invite them up sometimes. The volunteers usually don't get to sing. However, I do this for a living, and I CAN BE BOUGHT.
Even with a large tip though, I never let anybody take over. The audience will put up with anything for one song. If the guest doesn't want to gracefully get down, I just turn the mic off and tell them it quit.
DonM