[greenhatman]

Paying 3rd parties for gold, items, or xp was a Diablo 2 thing. They specifically designed Diablo 4 to make this hard to impossible.

You can't trade legendary items. They're account bound. And if you're trading lots of gold you get banned.

[BlueTemplar]

It was even a D3 thing already, remember the RMAH ? The main reason why (almost) all ActiBlizz games are online only is to make cheating harder. (They are particularly victims of their own success here, less popular games have it easier.