The main practices that are prohibited are usury, ambiguity in contracts (gharar), gambling and games of chance (maysir), fraud, bribery, the use of false weights and measures, taking others property unlawfully, and transactions on prohibited (haram) things.
What are all the haram things in Islam?
The religious term haram, based on the Quran, is applied to: Actions, such as cursing, fornication, murder, and disrespecting your parents. Policies, such as riba (usury, interest). Certain food and drink, such as pork and alcohol.
What does Allah not forgive?
Indeed, Allah does not forgive associating others with Him in worship, but forgives anything else of whoever He wills. And whoever associates others with Allah has indeed committed a grave sin. Despair not of the Mercy of Allah: for Allah forgives all sins: for He is Oft-Forgiving, Most Merciful.