Because taken with again, is on the level (7)
I believe the answer is:
sincere
'on the level' is the definition.
(I've seen this in another clue)
'because taken with again' is the wordplay.
'because' becomes 'since' (both can mean as a result of).
'taken with' means one lot of letters go next to another.
'again' becomes 're' (prefix meaning 'again').
'since'+'re'='SINCERE'
'is' is the link.
(Other definitions for sincere that I've seen before include "Honest, heartfelt" , "Candid" , "Showing genuine feelings" , "devout" , "Free from deceit" .)