The one who pays is always right (8)
I believe the answer is:
customer
'the one who pays is always right' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for customer that I've seen before include "One who buys goods or services" , "User of, eg, a shop" , "Person paying for item or service" , "Rail passenger, nowadays" , "Person buying" .)