I'm going to be brutally blunt with this and I apologize in advance for it.
We could add loads and loads of ways to counter scamming, but the strongest and most efficient way of countering it;
is to use your brain.
Being able to identify a scam is a life lesson IMO, and if you cannot identify a scam on
Minecraft then it's going to be extremely harsh on the outside world.
-Know the person your trading with
-Make sure they have a good reputation
-Never go first (unless you're extremely confident that you won't be scammed)
and analyze the person you are trading with if they are acting strange or extremely desperate just go with your instinct and play it off safe.
The idea you suggested, it sounds good but it is extremely unnecessary and unneeded.
I struggle to see the IRL trading side of the system, how can you trade IRL money for something in-game on a GUI, if it is a physical item then it holds risks of dupes and all the problems start from there really.
The idea is just over-complicated.
I won't lock this thread because I am curious to see what everyone thinks of it.