Rogue in favour of splitting money returned (9)
I believe the answer is:
reprobate
'rogue' is the definition.
(I've seen this before)
'in favour of splitting money returned' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'splitting' indicates putting letters inside.
'money returned' becomes 'rebate' (a rebate is an amount of refunded money).
'pro' inserted within 'rebate' is 'REPROBATE'.
(Other definitions for reprobate that I've seen before include "immoral" , "Rogue" , "Miscreant" , "Villain" , "17 [WRONGDOER]" .)