Coffee shop's hidden charges (4)
I believe the answer is:
fees
'charges' is the definition.
(fee is a kind of charge)
'coffee shop's hidden' is the wordplay.
'hidden' indicates the answer is hidden within the clue.
'FEES' can be found hidden inside 'coffee shops'.
(Other definitions for fees that I've seen before include "Lawyers' charges" , "Emoluments" , "School payment(s), for example" , "pay" , "Service charges" .)