Taxable service by stock brokers clarified: principal-to-principal trades not taxable, investor-facing transactions are taxable under service tax. Clarification that taxable service by stock brokers depends on provision of service to an investor: principal-to-principal trades between member brokers are not taxable; broker transactions on own account with a non-member investor are taxable; arbitrage between brokers of different exchanges is taxable as service to an investor.