Rating mostly dubious pricing system (6)
I believe the answer is:
tariff
'pricing system' is the definition.
(list or system of prices or charges)
'rating mostly dubious' is the wordplay.
'rating' becomes 'tar' (both can mean a sailor).
'mostly' means to remove the last letter (most but not all of the word).
'dubious' becomes 'iffy' (I've seen this before).
'iffy' with its final letter taken off is 'iff'.
'tar'+'iff'='TARIFF'
(Other definitions for tariff that I've seen before include "List of customs duties" , "Duty charge" , "List of duties on imports or exports" , "List of fixed charges as in hotel" , "Fees schedule" .)