What is the meaning of "Woe to the defrauders"?

Ibn Jarir said: "'Woe' is a valley flowing with the pus of the people of Hell, and it is for those who diminish people's rights in measure and weight." Al-Qurtubi said: "'Woe' is the severity of torment in the Hereafter, and it is a valley in Hell in which the pus of the people of Hell flows." The mutaffifun (those who give short measure and weight) are those who diminish measures and weights. It was also said that it includes tatfif (shortcoming) in everything, such as prayer and ablution.