Up until 2011/2012, all the slams had public draws where the players were drawn like a lottery, with a ball machine:
Then they dropped this method and went to pulling names out of a box. Both methods would be harder to rig, obviously. Then the USO started just presenting the draw to the public as already determined. So they announced an already predetermined draw! Then the other slams followed suit. I think the FO was the last draw to actually have a person involved in drawing names while being filmed.
I never believed in rigged draws until the last few years, and now am 95% convinced they are utterly rigged and done so to perpetuate the slam race.