Please note that Service Tax liability is always on receipt Basis.It is payable on The Gross Receipt which includes your profit / Margin also. AS asked by you after providing discount, if you raise a bill of Rs 9,300/= + Service Tax (10.30%)958/= comes to Rs10258/= & receives the same amount i.e. Rs 10,258/= from your Customer. You will be liable to Pay ST of Rs 958/=. However, if your customer pays you lesser amount (whatsoever reason), your liability of ST will be proportionately reduced.
The ST Liability is always on the ACTUAL RECEIPT BASIS & NOT on Billing Basis.