It is customary in St. Louis, and if you don't tip, there won't be an
available appointment in future. (Some of those folks are pretty
snooty.) In smaller towns, sometimes yes and sometimes no. If it
were me, I would tip, the sole exception being if the grooming is just
a part of a few days of boarding. You might find that the $2 to $5
you tip will go a LONG way in the future.