have a glib tongue 巧舌如簧

“巧舌如簧”，汉语成语，字面意思是“舌头灵巧得就像乐器里的簧片一样（The tongue is as nimble as a reed in an instrument）”，形容能说会道，善于狡辩，可以翻译为“have a glib (plausible; silver) tongue”，通常含贬义。

例句：

这个巧舌如簧的商人把次等品说成优等品。

The glib-tongued businessman described inferior products as superior ones.

他那么巧舌如簧，以至于骗过了所有的人。

He was so plausible that he conned everybody.