Just a short note on "knocker" in the sense of someone being a hawker, a door-to-door salesman.

Down here in Brighton (UK), a "knocker-boy" is someone who knocks on doors asking if the owner has any belongings - pottery, clocks, household objects, etc. - to sell. They usually work in pairs and are never to be trusted. They look round the house and, if they spot something of value, they tempt the owner by offering to buy something else of little value for more than its worth - praising it to the skies - then say something like, "Oh, and we could take that little thing (the valuable object) off your hands... not worth much... etc."

Not so common these days as people have got wise to most of it, but they do try it on with old people sometimes. Brighton is a local centre for the antiques trade, and knocker-boys had a very unsavoury reputation, verging on the criminal.