There is develiping game called Illarion, in which pking would have to be your intent.
Let me clarify, when two people fight each other one or possible both of them (depending on certain factors of the fight ie, poison, magical effects) would be rendered unconcious. They would lie there for a period of time unless they were healed, while they are lying there their body is available for looting. In order to pk you would have to target the unconcious body and attack again.
I propose we use a similar system, with the additions of
Looters get penalized, IE higher good npc\'s charging higher prices, a period where they may be looted without penalty, and if they loot enough then they should be allowed to be pked without penalty. Attention could be given to them by bounties being placed on their heads.
Giving people the ability to loot without having to kill should cut down on a lot of pking as you wont really gain anything by killing a player
Pk\'s should be available to loot and kill without penalty.
This system would be nice in that looters and pkers would have to lay low if they wanted to survive, and they would have to go after people who were alone unless they were extremely strong. By offering players the abillity to loot, and kill, it would encourage players to stick together for safety and potentially build up the rp environment.
A side note on looting, they should not be able to take all your items/armor/weapons perhaps as Tibia does the player should lose everything in their bag and possibly a random item they were wearing.