Leviticus 25:15-17

You are to buy from your own people on the basis of the number of years since the Jubilee. And they are to sell to you on the basis of the number of years left for harvesting crops. When the years are many, you are to increase the price, and when the years are few, you are to decrease the price, because what is really being sold to you is the number of crops. Do not take advantage of each other, but fear your God. I am the LORD your God.