Terms of Middleman trading.

1.I can't trade whose items-they're not mine-i can't do anything with them if the trade is in a system of something for something.
2.Trying to scam me goes with me blocking you.

How will the trade work?

First the guy num.1 gives me his item,then the guy num.2 does the same thing then I am just
giving out traded items.
It's simple!