Maturity test

To test the maturity of a watermelon when you buy it, you have are 3 possibilities:

Melon
Knock
You can knock on the melone: Mature melons have a singing sound, immature ones sound metallic light.
Weighing
Mature melons have more weight than immaturity ones.
Sight
A fair batch spot is an indicator that the melon was not rotated when it was growing.