The Hebrew behind "just weight" is more concrete than the English, and the phrase ties this verse to the Law.
Quick answer
Rigged scales are not a small sin in this book. The verse puts commercial fraud in the strongest category it has, and pairs it with something God takes pleasure in.
Read both lines
The two lines are a matched set: what the LORD detests and what delights Him, an opposition this chapter will repeat word for word at verse 20. What makes the verse land is where it puts the weight. This is not a temple matter or a private one; it is a merchant's bag, and the strongest religious vocabulary in the book is aimed at it. The NKJV footnotes "just weight" as literally a perfect stone, which is exactly the language of the Law: "You shall have a perfect and just weight" (Deuteronomy 25:15), and Leviticus requires honest scales, honest weights, honest measures. The prophets kept the same complaint alive. Business practice is treated here as worship, and there is no version of this book in which a person's dealings and their standing with God run on separate tracks.
Related: Proverbs 11:20 · Deuteronomy 25:13–15 · Leviticus 19:35–36 · Micah 6:11 · Proverbs 20:10
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.