Duffer

anything of no merit. A term applied by artists to a picture below mediocrity, and by dealers in jewellery to any spurious article. It is now general in its application to a worthless fellow.
a hawker of “Brummagem” or sham jewellery, or of shams of any kind, a fool, a worthless person. Duffer  was formerly synonymous with dudder , and was a general term given to pedlars. It is mentioned in the Frauds of London  (1760) as a word in frequent use in the last century to express cheats of all kinds.