Imam Amir-ul-Mo'mineen Hadhrat Ali (a.s.) narrates form the messenger of Allah who said:
He who is in business and buys and sells things must avoid Five Traits, otherwise he should not buy or sell anything :
1. Usury,
2. Taking oath,
3. Concealing the faults or defects of the goods,
4. Praising it wrongly when selling it, and
5. Finding faults in it when buying it."
(Al-Khisaal by Shaikh Saduq, vol.1, p.286)