Careless agent must accept cut (6)
I believe the answer is:
sloppy
'careless' is the definition.
(I've seen this before)
'agent must accept cut' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'must accept' indicates putting letters inside.
'cut' becomes 'lop' (lopping is a kind of cutting**).
'spy' going around 'lop' is 'SLOPPY'.
(Other definitions for sloppy that I've seen before include "Casual; sentimental" , "Lacking neatness and order" , "Mawkish" , "Slipshod" , "Romantic" .)