Green’s Dictionary of Slang

1. (US) to act in a sophisticated, wordly manner; to be cunning.

1928

D. Hammett ‘This King Business’ Story Omnibus (1966) 120: After twenty years of scheming and slickering in big-time cities, I let myself get trapped in this hill village.

2. to trick.

1954		K. Vonnegut ‘The Powder-Blue Dragon’ in Bagombo Snuff Box (1999) 155: Well, you’ve been slickered, dear, because the man was lying about his car.
1979		(con. late 19C) J.T. Edson Gentle Giant 78: You’d’ve knowed to ask where the backhouse was and gone afore they got a chance to slicker you into buying for ’em.