Bosch has oil filters/air filters/fuel filters/spark plugs/wiper blades and other stuff for all brands like Maruti ,Honda,Hyundai and Tata-atleast that much I know cause I use them. Bosch may not be the OEM
supplier for all the companies but their parts are equivalent or sometimes even better. For companies like Tata and Maruti sourcing common OEM
service parts is very easy. You might have to do a little homework for other brands.
With regards to services you can offer:
-Tyre change/wheel balancing
-Car Dent and Paint service
-Auto Insurance Renewal Service
-Car Grooming Services
-Used Car evaluation service-where you help people with buying used cars by checking them.
Regarding how much dealers charge,I can vouch that Tata and Hyundai labor charges are really high. The best people who will tell you about other brands are fellow TAI
-gers itself. Make a study-Ask fellow members who own different brands: "what was your last service bill?" you will get your answer.