Fixing dented bumpers

My friend does bumper straightening for a living. He pulls the bumper off and lays it face down on a large piece of carpet. He can see the dent, it's now a high spot on the back side. Using a series of hammers and dollys, he beats the high spot down until it's flat again. Sounds crude, but that's how he does it. If you want show quality, ship them off and have them done.