I always refer them back to the agent with agency, and I certainly expect the same from others

It's both. I always call the other side & inform them of the buyers conduct & let them handle it from there.

My 'spidey senses' say that this buyer will be a pain no matter what.

the listing agent should not be discussing anything with the potential buyer....and should be contacting the buyer's agent to control the buyer....

I let the buyer agent know what their clients are up to!

Oh, absolutely,.,I am a big believer in the karmic consequences of not doing the right thing, even if my client doesn't.

As far as answering the question in bold - I'm not sure what catagory you want to put it under but I would go with "do the right thing" and "treat your peers how you would want them to treat you".

Personally if I were the listing agent I would have told the buyers. "First you understand I represent the seller's interest and the your agent represents you, right?  So, I'm going to answer your question the same way I would answer it if your agent was asking the same question. (then I would either say make a written offer or if the seller had given me approval to communicate something less than what the listed price and terms are, then it is possible that I would answer their question with $$$ & X% closing costs) then I would ad that they should get with their agent if they have any further questions as their agent is representing their interest and can negotiate on their behalf which I can not do while representing the seller".

Paul S. Henderson, REALTOR®, Broker, Tacoma Washington - I always want the buyer's agent to be involved if any such thing happens.

It is PROFESSIONAL COURTESY and ethical, too.

I typically tell the principal to go through their agent.  I'd then alert their agent.

If I knew these folks were working with another agent and especially if I saw that they were the ones that had made a previous offer with someone else, I would immediately let them know they need to work with their agent and also call the agent to let them know what had just transpired.

I would have responded the same way. Redirect buyer back to his agent and tell them that this not appropriate behavior or way to buy a home.

Sometimes we need to remind our clients how things work, and WHY they work that way.

I agree with Jeffrey Jones & others who say they should be referre back to their agent.

Good morning Paul. It happens, but nothing usually good comes from it, unless permission is given for whatever reason.

 This has so many unintended consequences . . . besides the several obvious points, the Buyer will always think SHE is the one who made the deal happen, that her Agent couldn't get it done, but she did, so why does she need an Agent?

The Buyer sounds as creepy as the Agent, but we've all had them. 

I do it because I would want to know and also to give the agent a chance to rein in their client and get them back under control.

Yes,

Professional courtesy but also ethics if the clients are signed to an agreement

Completely; this does happen more often than many might admit.

Always back to the agent ... advising about agency ... and that I cannot discuss it with them. 

I would refer them back to the listing agent. The agent needs to know in my opinion.

Definitely refer back - I would hope for the same professional and ethical courtesy

I would say professional courtesy not an ethics issue if they contact you.

Ethically? No. A buyer has the right to approach any agent they wish and the agent contacted has no ethical duty that I'm aware of to report back to another agent. Is it wise of the buyer to approach the listing agent? Probably not - that listing agent is still, presumably, acting in the best interests of their client.

Professional courtesy? Dang straight! I'd want to know if my client were doing this, as obviously they're thinking I'd dropped the ball somewhere along the line and we'd need to have a serious discussion. I'd sure make the call if I were that listing agent and would direct that buyer back to their agent.

~~~~

On a side note, I would have to wonder if the listing agent is authorized by their client to give out such information in a phone call? As a seller, I probably wouldn't give such authorization to my agent, but I do understand that some people might so that they don't have to deal with the details. 

They would be calling their own agent with a combination of ethics, professional courtesy and just doing the right thing.