#1 Scamming
Scamming other users is not allowed. This includes, but not limited to, tricking players into giving you items, deceiving players in trades, and lying to other players to gain an advantage. If you break this rule, then you will be warned, kicked, and possibly banned.
If you drop an item for someone and someone else picks it up unintentionally and does not give it back, this is not scamming. You are expected to take precautions such as not trading near other players and turning on teleport protection. However, if someone is trying to catch item drops, you are trading to someone else; this can be seen as a violation of S0#4.