Plug in stain for a disreputable person (3,3)
I believe the answer is:
bad lot
'a disreputable person' is the definition.
(I've seen this before)
'plug in stain' is the wordplay.
'plug' becomes 'ad' (Advertisement plugs products).
'in' indicates putting letters inside.
'stain' becomes 'blot' (synonyms).
'ad' put within 'blot' is 'BAD LOT'.
'for' acts as a link.
(Other definitions for bad lot that I've seen before include "Thoroughly unreliable person" , "rubbish at auction?" , "Crook" , "Rotten fellow" , "Disreputable person" .)