Call evidence of overspending unconvincing (7)
I believe the answer is:
dubious
'unconvincing' is the definition.
(thesaurus)
'call evidence of' is the wordplay.
'call' becomes 'dub' (both can mean to name).
'evidence of' becomes 'ious' (I can't explain this - if you can you should give a lot more credence to this answer).
'dub'+'ious'='DUBIOUS'
'overspending' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for dubious that I've seen before include "Ambiguous or suspect" , "Unsure, unconvinced" , "unreliable" , "Morally suspect" , "Arousing suspicion" .)