Exchange money, being paid half of stated price (4,3,3)
I believe the answer is:
quid pro quo
'exchange' is the definition.
(quid pro quo is a kind of exchange)
'money being paid half of stated price' is the wordplay.
'money' becomes 'quid'.
'being paid' becomes 'pro' (as in professional as opposed to amateur**).
'half of' suggests halving the letters.
'stated price' becomes 'quoted' (as in a quoted price).
'quoted' cut in half is 'quo'.
'quid'+'pro'+'quo'='QUID PRO QUO'
(Other definitions for quid pro quo that I've seen before include "Something given in exchange" , "reward?" , "Reciprocal exchanges" , "Reciprocal exchange (Latin)" , "Tit for tat" .)