I live in San Marcos too! The only dog grooming place I know that I would assume is good is at Williams Veterinary Clinic (Dr.Williams used to be the owner but Todd now owns it...they both work there). I have seen many pretty pups walk out of there! Its off of Hunter road...the address is: 150 Quail Run.
San Marcos, TX 78666
512-396-1996
The people there are very nice! Hope this helps