There are many restaurants in Tamarindo near the beach. On all of our visits we found mariachi bands going from one to another, playing a few Mexican songs and asking for tips. It's optional but I always give them something. The music is pretty good and it seems like a hard way to make a living.
As a rule, the performers are pretty cheerful. However, the affect of this accordionist told me that something was weighing him down. He never smiled, but he still played well.