Belief in purchasing power (6)
I believe the answer is:
credit
I believe this is a double definition.
'belief' is the first definition.
(thesaurus)
'purchasing power' is the second definition.
(someone in credit has money they can spend)
'in' is the link.
(Other definitions for credit that I've seen before include "Praise; tick" , "good grade" , "good character" , "Time to pay, or due recognition" , "Favourable balance - good repute" .)