They don't actually define what "likely to be accessed by children" or "a reasonable level of certainty" really is.

I could say "some kind of attempt" is merely asking the user if they are over 18. I see no language that says that's not good enough, especially appropriate to the "risks" of 98% of websites.

> Where are you seeing that?

The noncompliance is on the part of the site owner, not the user. It just means you must ask their age (bracket), it doesn't mean the user has to tell the truth.