the.com/slicker

means A slicker is a person so smooth, polished, and persuasive that you can't quite tell if they're charming you or conning you — often used for con men, salesmen, or city folk with too much shine.

from Comes straight from 'slick,' meaning smooth or oily, which traces back to Old English 'slician' (to smooth) — related to words like 'sleek.' The literal sense of slick, greasy surfaces slid into a figurative one: a 'slicker' was someone whose manner was so frictionless, so polished, that they could glide past your defenses. By the 1800s in American English it had curdled into slang for a flashy, too-smooth operator — the kind of guy whose handshake you'd count your fingers after.