I don't mind this being a pvp server, but let's get the definition of Player versus Player down.
PVP is two or more players, all armed with some form of weapon, standing to fight;
NOT
a player entering a player's shop while they are selling something and kill them because they weren't served promptly
OR
Offering to sell somebody something and then kill them when they don't buy.
PKP isn't fun, and shouldn't be allowed, except for those who have made it their job to assassinate people on the server.