The fact someone has been in a movie, or more, does not mean that they know the ropes. There are lots of rumors and a many of them are way off. The fact that you do reenacting for free has nothing to do with the movie business, any more than helping a friend build a barn would have anything to do with a construction company wanting to hire you to help build a building. Your time and experience are worth money and if you take part in a money making project you should be reimbursed. They are extras, stuntmen and actors.
Extras are the people in the background, usually with little or no training.
They are the people in the crowd, walking across the street, sitting in the restaurant, etc. Stuntmen are the people who do stunts. These stunts can be as simple as fight scenes or hard riding to body burns or high falls. Stuntmen and Actors are trained and experienced professionals. The wages depend on area of the country and whether it is a union shoot.