If you are referring to the Varmint Hunters magazine club, you must have your shot witnessed by another member. Other than that it is based on a honor system.
When I was first getting into the longrange game I shot a crow @ 495yds (lasered & witnessed) with my 6mmAI heavy varmint rig. My buddy was so excited because he figured that I would be the first guy that he knew that would make the 500 yd club. I hated to disappoint him but although I was rather proud of the kill it still wasn't 500 yds and I wasn't about to claim it was. You know - like taking pride in a beautiful 10 pointer even though you killed it with the bumper of you 86' Chevy. Suggesting that it was your bow kill really doesn't do much for your ego.