Buy clay pot

The sun was scorching, and a blind man wanted to buy a crock pot, so he came to the open-air bazaar. The blind man asked a stall owner: "What color do your earthen jars have?" The vendor replied: "The earthen jars I sell only have two colors, white and black." The blind man asked again: "A earthen jar requires How much is it?" The hawker replied, "A white earthen jar costs three cents, and a black earthen jar costs two cents." After hearing this, the blind man said, "Then give me a white earthen jar!" The peddler handed the jar to the blind man and collected the money.

In fact, the hawker bullied the blind man and couldn't see it, and actually gave him a black jar. The blind man took the jar, touched the jar on the ground again, and said angrily: "I am blind, you bully me and can't see, you will lie to me, use a black jar to fake a white jar, go! Let's go to the police Bureau, you have to double the compensation to me."

Excuse me, how did the blind find out that they were deceived?

[Reference answer]

After sun exposure, the temperature of the white can is lower than that of the black can.