The purpose of restaurants, pubs & clubs booking performers and bands is to provide alternative entertainment for their regular patrons. Do not expect to have dinner and a show, as the core function of these establishments are for people to get together, and drink. It is usually very loud.
As an artist it is a great platform to refine your performance set. Connect with new audiences who will enjoy your music through the noise. Be mindful of the fact that these are not listening venues. Do not get upset with a disengaged audience, lack of payment and adversity to particular genres.
Venue owners are usually looking for something specific and will rather book an amateur artist to provide the entertainment suitable for their establishment. Nevertheless, use the opportunity for what it is. Understand that it’s not a professional and well-paying gig but you can still make the best of it!