sell someone or something short

sell (someone, something, or oneself) short

To undervalue someone, something, or oneself; to underestimate or underappreciate the good qualities of someone, something, or oneself. Often used in negative constructions. Don't sell yourself short—your writing is really excellent! I know you don't like their pitcher, but you shouldn't sell him short. He's actually got some of the best stats in the league. I think they're selling this short. It's actually an incredibly good deal!
See also: sell, short
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

sell someone or something short

fail to recognize or state the true value of someone or something.
1998 Times Mr Ashdown may secure his seat in the Cabinet, but he will have bought it by selling liberal principles short.
Farlex Partner Idioms Dictionary © Farlex 2017
See also: