The fact that the Zuckerberg ad was rejected seems to indicate that they really were being put through a vetting process. It's possible they are vetted again after payment is received but that seems unlikely.
Occam’s Razor - it’s knocking on your door, asking to not be quoted when you’re not actually using it.
I believe the parent comment was claiming there is no general filter and/or vetting for others - only for Zuck.