duffer n.

"inept person; stupid, dull old man," 1842, especially "bad golfer" (by 1875), perhaps from Scottish duffar "dull or stupid person," from dowf "stupid," literally "deaf," from Old Norse daufr, with pejorative suffix -art. Or perhaps from 18c. thieves' slang duff (v.) "to dress or manipulate an old thing and make it look new," hence duffer "one who sells spurious goods at high prices" (1766).