Authorised service station

As per my knowledge like other Service Providers basic exemption from service tax is also applicable to Authorised service stations. It's only when you cross the basic Threshold limit you become liable for payment of service tax. Please refer to point (G) in the link below:

https://www.servicetax.gov.in/st-profiles/service-stns-motors.htm

Hope this helps you.

The case would be different if you are providing a service under any brand name, because in that case the exemption would not be available.