It depends a lot on the server like for example Existence Ragnarok Online uses its own unique pvp system which track's player's kills and gives them an aura which other players can see to warn them the person is dangerous and has been killing too much. As the points scale the aura color changes:
Red Aura 100-199 Blue Aura 200-299 Black Aura 300+
When a player hits 300+ and is killed by another player its possible they could drop some items and they are set directly to jail where they have to wait for points to drop or bribe the jailer to let them out sooner. Player's who have killed too much can hide in market or paradise island and wait for points to drop.
Players who pk others get experience and part of another players money that they are carrying people that kill others who have been killing too much gain a higher rate of experience and money.
Money which is given to the person going around pking others is automaticly set into a bounty system over that players name. In the future others will be able to take a quest to kill that player and can claim the reward for doing so.
As you can see this is a specific type of PvP not the average pvp you would find in retail or most private servers because it was customized.