Selling

I recently moved in with my mom and I am trying to down size her stuff. The storehouse is full , house is full and the carport is full ? Going through all the boxes, shelves and trying to get everything dusted off and organized to sell. WOW, what a big job, how does one woman have so much stuff, antiques from her store, collectibles she has collected over the years and all the project material that where stored for projects but, never made ?? I will need therapy after all this , any suggestions ??