Before you book a singer, find out if they perform to pre-recorded music on a karaoke-type machine. While this doesn't necessarily invalidate their talent and may not bother you, to some observers it might appear unprofessional, if not actively cheesy.
One fun option when hiring a singer is to hire a professional imitator. While most people are familiar with Elvis imitators, there are also plenty of Tom Jones, Cher, Barbra Streisand, and Madonna imitators out there, not to mention hordes of others.
