Commission sources (5)
I believe the answer is:
sales
'commission sources' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sales that I've seen before include "Occasions for buying at reduced prices" , "Periods when shops offer goods at reduced prices" , "Public auctions" , "Periods of price reductions" , "a feature of Boxing Day?" .)