Resent a criminal being sincere (7)
I believe the answer is:
earnest
'sincere' is the definition.
('earnest' can be similar in meaning to 'sincere')
'resent a criminal' is the wordplay.
'criminal' is an anagram indicator.
'resent'+'a'='resenta'
'resenta' anagrammed gives 'EARNEST'.
'being' is the link.
(Other definitions for earnest that I've seen before include "Firm" , "Serious - money deposit" , "See 1" , "Sincere; determined" , "serious attention" .)