How about creating an NPC that give you a quest of killing some monsters?

for example, you are level 30, he sends you kill some monsters of your level and up, for example, 10 slimes and 5 rats,and so on... and he reward you with money and experience. something like a bounty hunter.

if you guys allready played rappelz , i am talking about the quest client in every town.

imagine, your pal is at the same time killing the same amount of mobs of the same kind in the same time. he is getting their loot, as well as you do.
now, why would you be rewarded with money and additional experience?

well, for leveling up. but thats ok the XP only for killing, but money rewards can help a lot of people.

ok, i admit this was a tricky question in fact i wanted you to improve your idea. cause still, why you get money and other people doing the same hunts (without qeust) don't?

boo, we don't need more money, our economy is broken enough, save us wipe!

ok, but how about some items, normal and expensive ones, but normal.
or just quest for fun.

This same thing already happens with quests. Players can kill the mobs (e.g., minotaur king) that other players on a quest can kill and just get their 150 copper pieces, but the players on a quest get so much more than that .... why would it be any different? The difference is that players on a quest have taken time to explore and speak with NPCs, even more than once. They're playing the game more, and not just grinding.

I like this idea, though I'm not sure how difficult it would be to implement at this time.

For one, it would take some of the monotony out of the hack and slash leveling experience.  Gives the player a purpose, and perhaps a short term goal which will eventually help achieve the longer term goal of leveling to 110.

Here's a novel idea though.  Rather than experience in a combat skill, perhaps this could be an alternative to trap training, (or in the future as other unused skillsets are implemented, other skills.)  Anyway, there's lots of reward options, booze, weapons commensurate with level and therefore task, and perhaps straight up cash.

One of the best benefits that occurs to me, however, is information.  By taking these generic quests, players may learn about training areas, (by finding the mobs that they are tasked to hunt down,) which they may not have otherwise been aware.  How often do we hear the question, "Where is a good place for a level xx to train for good experience...?"  Well, if there's an NPC who gives a quest based on your level, this could be a great way for this information to become self-evident.

One thing is certain, the rewards should be commensurate with the difficulty of the quest.  If the NPC is designed to give the player same leveled mobs or send them to easy dungeons relative to their level, then the rewards should be quite light.  OTOH, if the NPC gives a tough quest, with purple mobs in a dangerous dungeon, the rewards should be...well, rewarding.

Well my thought on this idea was ; 
 the guy would have to have a completed list,also visible by the player and not other players and a counter on how many times you have completed each task also the bounty would have to go down for each time you did each bounty the color chart would be great for this cause once you have done the bounty enough times say like gray you start paying him to take the bounties,at which, what ever the (gray) bounty for you,you would receive a    "I am a <quest> Bounty Hunter Champion"