1 Thessalonians 4:6
That no man go beyond and defraud his brother in any matter: because that the Lord is the avenger of all such, as we also have forewarned you and testified. That no man go beyond and defraud his brother in any matter: because that the Lord is the avenger of all such, as we also have forewarned you and testified.
The command forbids going beyond and defrauding another person in any matter, and that includes taking advantage of a fellow believer in business dealings. It reaches dishonest business practices, false pretenses, and any disregard for truth and integrity. Such deception is not to be boasted about or excused as business sharpness.
Charging exorbitant interest to someone who urgently needs help is that kind of fraud and dishonesty. The prohibition also includes injuring a brother by false testimony, by misstatement of his words, and by anything that has harmed his influence. Wrongdoing of that kind must be made right by correcting the statements with the people who heard them.
Taking advantage of a brother is contrary to the conduct of God's children, and hope of future blessings gives no reason to do so. Such conduct is recorded in heaven and shows that a person is not governed by the principles of Christ's gospel but reflects the adversary rather than God's Spirit. Those who will inherit the heavenly kingdom must be transformed by divine grace.