Amount Collected more than the MRP in all shops in Dindigul.

Hi,
My father bought 2lts Bovento Cool Drink bottle in a shop which is
in Bus stand complex of Dindigul, Tamil Nadu. The shop keeper asked
Rs.60. But the MRP in the bottle ws Rs.50. My father asked the
explanation for the deviation in the rate. But he didn't explain and
didn't reduce the amount also. In all the shops at the bus stand did
the same. Is it possible for me to know the reason behind this??