I spoke to my manager recently about something similar.  I got a call to show a home I had listied a couple of years ago, and now happened to be on the market with some one else in my office.  (which I was fine with, by the way).  the guy said he had a agent, who was a neighbor, but he went out and looked at homes, and if he saw something he liked, the neighbor would write it up.  He said he had nothing in writing with the neighbor, nor would he sign a broker/buyer agreement with me, though he verbally said  he was fine with me giving his neighbor a referral fee.  (I know, that agreement is worth the paper it was written on.)  Anyway, my manager said I would have to show an ongoing relationship with that buyer to get procuring cause.  But enough about me.

There are certainly ethical, if not legal, issues with the scenario you wrote about, and as the discussion with my manager showed, one showing may not be enough for procuring cause.  If the "associate" is  a partner with the listing agent, or an assistant, why is s/he so insistant on the double pop?  I know listing agents that will not "double end" a listing because of potential conflict of interest, but will refer the buyer to someone else,  The listing still get a referral fee, so make some money, the buyer has an agent dedicated to them in negotiations.  Seems like a win'win to me.

If I were the buyer on the above situation, my gut would likely say "I feel like my arm is being twisted here, and I don't like it."  Personally, I don't like pushy people, agents or otherwise.  AS opposed to telling the buyer how it was going to be, some discussion about what the buyer was looking for, and how they could get it may have been a better approach.