I did not think that it was unethical for him to advertise on Zillow, it was just a learning experience because I thought I was calling the listing agent. Lesson learned. If I wanted to use a buyers agent, I have one here that I've known since 1st grade. That was 1966.
I also have no interest in screwing the kid out of his commission, as I plainly stated in the OP. I'm simply asking about the ethics of dealing w the listing agent directly. He has all the info I need. Time is of the essence.