Do you wanna know how the shops dupe there items?

[Jazon]

The server calculates what kind of item and the item's stats when a monster dies. Nothing is done on the client side. The only packet that gets sent when an item drops is to tell the client to display the animation.

And sending packets is way more safe than altering memory, as long as you send valid packets.

Nothing is done on client side yes, thats true. But it is not client side sending, imo they stop the packets sends to the client before it is recieved by the client, transform it somehow and sends it further to the client.
Dont ask me how this can work, i only heared of this and it is making sence to me for the stocks of same items with unique id tags.