Normally a broker (listing or selling) is ONLY entitled to what is agreed under the written contract. Depending on what the dollar amount is, you may want to sue under Small Claims Court and take your documentation and timeline, logbook etc. into court to show the Judge. If the amount exceeds the Small Claims ceiling, you can sue for Breach of Contract, Breach of Fiduciary Duty, etc. Look on Avvo.com for either a Real Estate attorney or a Litigation Attorney in Santa Barbara. Good Luck on your case!
You need to take a look at the Listing Agreement between yourself and your broker. Many standard agreements do have provisions for brokers to collect some commissions when a buyer prevents the closing. But, you need to check the language of the Listing Agreement and see how that language apples to the facts of your case. If you want to send me listing agreement next week, I can take a look at it for you.
However, since your agent told you they would not take any part of the deposit as their commission prior to your signing the cancellation, they probably can't take any part of the deposit because you accepted whatever split of the deposit based on our agents representations. Your agent and broker have a fiduciary duty to you and your entitled to rely upon their representations to you and they have an obligation to put your interests above their own.
That listing agreement also will state the duties of the brokerage. Generally speaking, it is not your duty to negotiate your own transaction as that is why you hire an agent. You shouldn't even speak to the Buyers directly unless it is with your agent present.
If your not happy with the broker or agent, then check your listing agreement and see if they provided all of the services they promised for the commission they expect.
Kevin A. Spainhour, Esq. Spainhour Law Group www.slglawyer.com.