Cheating in business shows lack of faith

 Netziv (Devarim 25:17): However a person who uses false weights doesn’t do it from lust. He does it because of a lack of faith in G d who feeds and sustains through Providence according to one’s deeds. Thus the sin of false weights is an aspect of idol worship. Therefore the sages said that the sin of false weights - even though it is just an aspect of idol worship and is far from being outright heresy. Nevertheless it is more severe than lust which produces sexual immorality. This is because a lack of faith is difficult to repent and because it is relevant to G d’s honor. Now how does all this relate to Amalek and the astounding fact that doubts arose in their hearts despite having witnessed so many miracles? We have explained that they had doubts that G d was with them in nature after the miracles ended. Because they had a lack of faith in G d  - Amalek came. The sin of false weights is used as an example of lack of faith.