I know for any of my "tournament for dummies" for players rated 1500 or below, about a day or so before the tournament starts, I actually go through manually and kick out anyone who is way above 1500. (If someone now has 1525 or something close I usually let them stay - but if it's like 1700, then they are gone.)

But even then, some are unrated and even within hours of it starting they can shot from unrated to 2100.