When you sell someone short what you are doing is underestimating the individual. You fail to see the redeeming qualities of the person. The expression, which is mostly used in informal contexts, can be applied to objects as well.
Here are a few examples.
* This is a really beautiful house. Why do you sell it short?
* When you say that Vijay doesn't know anything about painting, you are selling him short. Do you know that he is one of the most respected art critics around?
* If I were you, I wouldn't ask Bala. He always sells people short.
COURTESY : The Hindu (The National News-Paper) - India