James: a real estate agent that represents the seller, is only due a commission, once the contract is signed by all parties concerned, and the deal closes escrow.
Many things can happen after a contract is signed but before it closes escrow, some examples are, No Loan, house has major inspection faults/repairs, and low appraisal value. Always look at the listing contract that you signed for information on what your duties and rights are.
In the example cases shown above, a deal would fall through if the buyer is unwilling or unable to bring more money to the table and/or the seller making repairs, and no commission is due.
The only way that a selling agent is due a commission, without the seller signing, is if the buyer comes with a contract offering you your asking price, and no other terms/stipulations. ie. Example, your asking price, 30-45 days usual closing time, no loan contingency, no inspection contingency. Of course, what you wrote in the listing contract, is what stipulates your asking price and contingencies. Most have 3% down, 17 days for home inspections, and a loan contingency. So, check your listing contract to know what you had contracted would be the terms that you had agreed to. A willing and able buyer with additional terms is not what you agreed to in the listing contract when you put the house for sale with the selling agent. I may be wrong, but I still have not heard or seen a listing contract that also included your consent for "and any other terms that buyer brings to the table".
Please note, that if you sign for a specified period of time, ie. 6 months, 1 year, etc., your selling agent is still allowed to market your property. Some agents may discontinue the contract with a disgruntled seller, but will need to provide you, the seller, with a written cancellation of the listing contract, signed by the agent and seller. Always talk or email the listing agent and let them know what your concerns are. You may be able to come to an agreement, or the listing agent may let you out of the contract as soon as possible.
Never hire another selling agent, until you have a written signed cancellation from the first selling agent. Otherwise, if your house sells during the initial listing contract period, you will owe double commission to each selling agent.
As to a buying agent, you can fire them anytime, but do provide some type of written notification via letter or email, to have written backup in case something comes up later on. Then, go and find another buying agent that will provide better assistance to you.
The majority of real estate agents are very knowledgeable and professional. In your case, it seems that was not the case. RE Agents are similar to cops. Cops have a bad reputation, but most are honorable, hard working professionals. One bad apple, does not spoil the barrel. Just look at the NYC cop that was caught in a photo helping a homeless person. The cop did not want publicity when he was doing the act of kindness. Most cops, and RE agents are like that. Too bad we don't hear about the majority that are doing good professional jobs.