The existence of the bunker isn't the issue; it's being let in when crunch-time hits. If management cant' control access, it's a sucky bunker that will be at considerable risk of attack in a disaster scenario. If they can control access, you are depending on them to honor an agreement enforced by a legal structure that is, presumably, currently dealing with bigger problems right now, if it remains functional at all.
I don't mean to allege that this guy specifically is planning on doing so; but those circumstances would make 'overbooking' a very tempting strategy. If disaster fails to occur, you merely need to conceal exactly how many spots you've sold. If disaster does occur, the people you do admit are unlikely to give up their spots to let in the ones you don't, and the ones that don't won't exactly have much recourse.
It doesn't help that, pre-disaster, the people with the most money are the most valuable potential-bunker-dwellers, since they can pay the most for spots; but during a disaster, and after, people with assorted useful skills are the most valuable potential-bunker-dwellers. There could well be some overlap, if some doctor who has made good in his practice can afford a space, he's also a useful guy to have around; but the post-apocalypse's demand for investment bankers is probably fairly low.