Answer:

1. Cheating: such as hiding the defect in a commodity.

Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) once came upon a heap of food, and when he put his hand into it, his fingers felt some dampness. So, he asked the owner of the food: "What is this, O owner of the food?" The man replied: "The rain had fallen on it, O Messenger of Allah." Thereupon, the Prophet (may Allah's peace and blessings be upon him) said: "Why did you not put the damp part on the top of the food so that people can see it? He who cheats has nothing to do with me." [Narrated by Muslim]

2. Riba (usury): such as borrowing one thousand from someone to be returned as two thousands.

This excess is the prohibited usury.

Allah Almighty says: {But Allah has permitted trade and forbidden usury.} [Surat al-Baqarah: 275]

3. Gharar (uncertainty, risk) and Jahālah (ignorance): such as selling milk that is still in the female sheep udder, or fish that is not yet caught.

The Hadīth states: "The Messenger of Allah (may Allah's peace and blessings be upon him) forbade any sale that involves Gharar (uncertainty, risk)." [Narrated by Muslim]