As far as I know there is no set rule against exchanging money on the bourse floor between on dealers.

With that being said we need to be respectful to our dealers who actually pay for thier right to sell on the floor. Attendees should not be interfering with a sale that someone is trying to make with a dealer or setting up thier own shop.
There is nothing wrong with approaching someone who is trying to sell chips to a dealer and making them an offer after a dealer has turned them down.

Now there is a strict rule about no cash sales at the trade sessions because of issues In the past with some people making trade session tables thier own version of a free convention table.
They would set up shop just like they were a dealer but pay none of the table fees like those across the hall.

On the subject of the bistro tables..... this was the first time that we had these tables in the back of the room. I believe there were flyers on the tables when they were set up asking people to not do any selling at these tables as we were afraid they may be used like the trade session tables were used In the past.
It could be that these flyers were covered up or maybe they were thrown away over the course of the day. However the intention was that no sales were to take place at these tables which would In effect be competing with dealers who paid for thier tables.

I have no comment on what actually happened as I was not a witness.

So, to sum things up, these types of transactions do still exist and there is no set rule against exchanging cash as as long as it's reasonable and not interfering with the dealers.

I hope that sheds more light on cash transactions on the bourse floor.