Charles Spurgeon Commentary Jeremiah 32:9

"And I bought the field that was in Anathoth of Hanamel mine uncle`s son, and weighed him the money, even seventeen shekels of silver." — Jeremiah 32:9 (ASV)

And I bought the field of Hanameel my uncle's son, that was in Anathoth, and weighed him the money, even seventeen shekels of silver.

They always paid by weight to make sure that the amount was correct.