Shouldn't be, but could be the case. In real estate, the laws are clear and not something you want to violate. In simple terms, Broker should represent one side or the other, put client's interests ahead of his own, and the side he/she does not represent should receive fair and honest treatment. Real estate Brokers are required to disclose any material defects to all parties including the side not represented. I am not aware of any laws that relate to aircraft Brokers though.
Have low expectations, the Broker is probably not going to help you at all, unless he/she is selling your aircraft or has been retained to represent you in a purchase, keep your guard up, don't tell the Broker anything that could be used against you (eg. I would really pay up to $100k but let's offer them $80k), take nothing at face value and question everything presented. Consider getting a professional to represent you, including negotiating deal. I negotiate every day for a living, and I do have an advantage due to my practice, regardless of what is being negotiated.
Just don't expect much from any Broker that is not representing you, and you will do better in negotiation, and you will rarely be disappointed.
If you have problems with a Broker that is representing you, that is another discussion.