1. Yes, you are liable to charge & pay service tax under Business Auxilary Services.
Read: Malabar Management Services Pvt. Ltd. v CST, Chennai 2007-TIOL-1949- CESTAT-MAD : 2008 (9) STR 483 (Tri. Chennai) – In the instant case, the appellant was engaged in marketing of ICICI bank's loan products through tele-marketing or contacting prospective customers as well as processing documentation and evaluating the customer and forwarding application to the banks. The bank was paying service charges on monthly basis for the same. The tribunal held that such activities rendered by the appellant to the ICICI bank are covered under the business auxiliary services.
2. For current financial year, whenever your commission receipt exceeds 9 lakhs Rs., you are required to get registered with Central Excise & service tax department. And charge collecting service tax @ 15% from every rupee above rs. 10L.
3. Well, you may get exempted under GST, as the limit there would be 20 lakhs.