Sell sb/yourself/sth short Verb + object/complement
To underestimate someone, something or oneself
Don't sell yourself short. You sing beautifully.
They're selling Ellie short because of her appearance, but they don't know that she is the best student of her class. Don't judge a book by its cover.
Used in response to a threat suggesting that the threat is a weak one.
To have low respect or regard for someone or something; To evaluate someone or something with a negative attitude
1. To consider something as true, real or available without questioning it
2. To fail to show proper appreciation or gratitude to someone or something; to underestimate the value of someone or something
The verb "sell" should be conjugated according to its tense.
Daughter: So I really want all my friends to have a great time. I was thinking it would be a good idea to have some candy out on the tables for people to snack on.
Mother: Well, if you want them to really enjoy themselves, candy is dandy but liquor is quicker.