Co-owner put up hire charge (7)
I believe the answer is:
partner
'co-owner' is the definition.
I can't judge whether this definition defines the answer.
'up hire charge' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'hire' becomes 'rent' (synonyms).
'charge' becomes 'rap' (both can mean blame or responsibility).
'rent'+'rap'='rentrap'
'rentrap' back-to-front is 'PARTNER'.
'put' is the link.
Can you help me to learn more?
(Other definitions for partner that I've seen before include "Mate or business associate" , "Spouse or business collaborator" , "Other half?" , "Consort" , "Companion at bridge, dance, or home" .)