Agree to have fiddle dispatched (7)
I believe the answer is:
consent
'agree to' is the definition.
(I've seen this in another clue)
'fiddle dispatched' is the wordplay.
'fiddle' becomes 'con' (both can mean a scam).
'dispatched' becomes 'sent' (I've seen this in another clue).
'con'+'sent'='CONSENT'
'have' acts as a link.
(Other definitions for consent that I've seen before include "Permission, agree" , "Agree (to do something)" , "authorisation" , "Agree or permit" , "Agree or comply" .)