If you are confident in your skills... just offer a single free performance to a few places.. have them enjoy them.. amd then ask them to book you for your normal price.
Bachus........that's a very good and practical idea on paper, but the odd thing (around here, at least) is when you offer a "free show" they think you're an amateur trying to get a start in show business.
BUT....that location where I had the difficulty with the AD that I just posted about. A friend had been telling me to call them for years......absolutely gorgeous place. So, finally I DID call them, volunteered to put on a show for nothing and I've been playing there regularly ever since. Other places look down their noses at anyone who asks if they can play for nothing.