Return of old item cancelling out husband's purchase (7)
I believe the answer is:
footing
'purchase' is the definition.
(thesaurus)
'return of old item' is the wordplay.
'return' says the letters should be written in reverse.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'item' becomes 'ting' (I can't explain this - if you can you should believe this answer much more).
'of' back-to-front is 'fo'.
'fo'+'o'+'ting'='FOOTING'
'cancelling out husband's' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for footing that I've seen before include "Plain lace" , "(Firm) basis on which something is established" , "Secure and established position" , "Status - relationship" , "Basis, foundation" .)