Forger seen in bar, assembling it free (13)
I believe the answer is:
counterfeiter
'forger' is the definition.
('counterfeiter' can be a synonym of 'forger')
'bar assembling it free' is the wordplay.
'bar' becomes 'counter' (I've seen this before**).
'assembling' indicates anagramming the letters.
'it'+'free'='itfree'
'itfree' with letters rearranged gives 'feiter'.
'counter'+'feiter'='COUNTERFEITER'
'seen in' acts as a link.
(Other definitions for counterfeiter that I've seen before include "person making money illegally" , "Forger" .)