Turnover, including source of cash, and balance (6)
I believe the answer is:
scales
'balance' is the definition.
(balance can mean a set of scales)
'turnover including source of cash' is the wordplay.
'turnover' becomes 'sales' (I've seen this in another clue).
'including' means one lot of letters goes inside another.
'source of' indicates taking the first letters.
The first letter of 'cash' is 'c'.
'sales' placed around 'c' is 'SCALES'.
'and' acts as a link.
(Other definitions for scales that I've seen before include "Weighing devices or fish flakes" , "Set of balances" , "7 [SIGN OF THE ZODIAC] representative" , "Libra, Sign of the Zodiac" , "Fish flakes or weighing instruments" .)