Is it Haram or Halal to work as a sales person in a car dealership? Is it permissible to work as a real estate agent?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

As long as you are acting according to Shariah (Islamic jurisprudence) in your dealings, then there is no harm for you to work as a car salesperson or an estate agent or any other permissible work.  There is also no harm for you to work as an intermediary between the buyer and the seller and it is permissible for you in this case to take money from one party or both parties according to the customs or according to an agreement between yourselves.

However, you have to be sincere and trustworthy; you should not conceal a fault, cheat or deceive any buyer.

Allah knows best.