Firm is no merchant holding dubious label (8)
I believe the answer is:
misnomer
'dubious label' is the definition.
(a dubious or inappropriate name)
'firm is no merchant holding' is the wordplay.
'holding' indicates the answer is hidden within the clue.
'MISNOMER' is hidden in the letters of 'firm is no merchant'.
(Other definitions for misnomer that I've seen before include "Inapt term" , "wrong title" , "the label's wrong" , "Wrong name or term" , "Is Norm me? (anag)" .)