Is working as a real estate agent in the United States permissible (halal)?

The basic principle is that brokerage in buying or leasing real estate and taking a fee for it is permissible, unless it involves assisting in something forbidden, such as brokering the sale or lease of a place for selling alcohol, usury, gambling, or musical instruments, singing, and dancing. This is based on the verse: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." (Qur’an 5:2). It is also considered assisting in the forbidden to direct a person whom you know will purchase the property with usury. However, if you do not know, then there is no sin. If the person has dealt with usury and brought the money, there is no sin in directing them to the property, because it is permissible for them to buy the property with usurious money (while they still bear the sin for the usury itself).