i-adjective
smooth-talking; glib; honey-tongued
Describes someone who speaks flatteringly or persuasively, often with a negative connotation of insincerity.
彼は口先のうまい人だから、気をつけたほうがいい。
He's a smooth talker, so you'd better be careful.
口先のうまいセールスマンにだまされて、高いものを買わされた。
I was tricked by a glib salesman and ended up buying something expensive.
Compound of 口先 (lip service, superficial words) and うまい (skillful). The phrase literally means 'skillful with the tip of the tongue,' figuratively describing someone adept at smooth or deceptive speech.