service tax liability on road transport agency

sir, i know that service tax liability is of service receiver in case of GTA.

i have query on this example.

i am a trader of coal.I debit freight expense both inward and outward in my books. But my some customers want FOR billing,so i includes the freight and servicetax amt in rates charged to them.. IS IT RIGHT ?

My some customers wants seperate bills for transportation and for sale. In transport bill i write that SERVICE TAX LIABILITY  IS OF CONSIGNEE . so is it right.  IS'NT IT IS OUR LIABILITY TO PAY SERVICE TAX AS WE R DEBITING FREIGHT EXPENCE IN OUR BOOKS FIRST.  

PLS REPLY.

THANKS