I do play online games for a long time now. And what really strange for me is cheats that exist in online games. They do exist - in wow it was at least movement speed, in aion it is attack speed, in lineage 2 it was an overbuff. Almost all of them had ability to dupe items.
As a web developer we have a first security rule - never trust user input. Why do online game trust client input?
Is it too expensive to verify all user inputs, but server has all the required information about everything that happens in game. Why can't it verify even statistically if something was fair or not?