shake-and-bake
Registered
That rates somewhere around a "zero" on my screw-up-o-meter.
Right before I walk/roll/fall off the side of the boat, the very last thing I do is breathe off both my regs, check my computer, inflate my BC and make sure it actually holds air.
If I don't have air or can't float, it's 100% my fault.
If an operator represents to its clients that it will set-up their gear in dive-ready condition, including turning on the air, knows those clients (however foolishly) may expect and rely upon them to do so, knows that if it fails to do what it promised to do a diver may go into the water without air, yet fails to perform the most critical step of the duty it has taken upon itself to perform, I can't see how it's contribution to the fact that a diver is in the water without air can ever be considered "zero." Its responsibility may be greatly outweighed by the diver's stupidity, but it ain't zero.