Lately, Maruti started pumping in more value added services like additives and flushes like Hyundai and SAs are pushing them more for incentives.
My experience with service centers are limited since I don't go there after free services.
Maruti was mixed response. Multiple visits for same complaints and improper troubleshooting. Gearbox issue with brand new car. Visited again and again and again. After shooting a mail, they came home, picked up the car, rectified and brought it back. Then a dead battery, which they never found the issue with. 2-3 times had to call RSA to jump start. They even said fault with aftermarket headunit and installed switch for HU. Finally checked battery on dad's advice. 7-8 visits to SVC for that.
Only once visited Tata. It was the early 2000s and they-were-**** era. The moron took the car to parking with a heavy wheelspin. Issue was check engine light. They kept the car for a week swapping parts with a new car, but no solution and to our surprise, they flew down engineer from Pune and got it fixed.
Later cousin was SA at Tata dealer and saw him calling customers for feedback in the evenings and never seen anyone yelling at him.
Maruti was notorious for stealing our stuffs and breaking things, mostly by the guys moving car from service and wash. @vishnuvichu lost his spare wheel (similar happened at Toyota as well). Usually door lock levers, boot/fuel lid release are the common things damaged by them. I even lost a pack of GEMS :p