In this business you get good gigs and bad gigs. Nevertheless, good can come of almost any situation. Me + my mate played a restauraunt once, for a serious fee (for the area and time). We played to the staff. Thats it. No punters. We played staff requests all evening and attempted to play as if the place was packed. I even ad-libbed a duet with the owners wife!
However... we picked up 2 private parties and the local annual dance because the owner was impressed with our music and attitude and broadcast our name.
All you can ever do at a gig is play your best. If no-one turns up thats a publicity or marketing problem (unless you really are terrible!). My sole measure of success is "the rebook factor". If places re-book you on a regular basis, you are getting somewhere.
remember - in this business there are no instant successes, even if it looks like it. The Britneys of this world paid their dues as kids.