If you want to request someone to help you, if you don't follow the official procedure, the player who accepts your mission will not receive any reward.
In order to ask for someone to do your own mission, you must talk to the NPC that is at the counter and tell him what the mission is. The NPC will respond, give it a rank, and then the other player may start the mission.
The person who requested the Help will not get any reward, even if he helped complete it. Any other player that does the mission will receive the reward like a normal mission.