Posted by Picky on April 28, 2012 at 06:10:32 user Picky.
In Reply to: Re: Duffers posted by Mike Field on April 27, 2012 at 16:18:41:
The Oxford English Dictionary says:
Duff, a noun meaning "Something worthless or spurious; counterfeit money; smuggled goods; and also the passing or selling of such things"; first cited (as slang) in 1781.
Duff, an adjective meaning worthless or spurious, first cited from 1889 as thieves' slang.
Duffer as a verb in Australia meaning, of a mine, to become unproductive or exhaustive, first cited in 1881.
Duffer as a noun meaning "One who sells trashy goods as valuable, upon false pretences, e.g. pretending that they are smuggled or stolen, and offered as bargains", first cited in 1756.
Duffer as a colloquial noun meaning "A person who proves to be without practical ability or capacity; one who is incapable, inefficient, or useless in his business or occupation; the reverse of an adept or competent person. Also more generally, a stupid or foolish person" first cited in 1842.
The OED reckons the words are all connected – and you can see the link with the rustler, too, I think.