As an agent, I can tell you can call her/his broker to

Complaint and ask to break the contract, you can also leave feed back after closing. 

You can also get a realtor license if you want to save commissions, I mensioned at a meeting that realtor's work is not worth that much and should lower commission rate such as 2 percent or less or, my supervisor replied "this is my full time work, I need to pay my bills...", remember commission is always negotiable.