Having the details of 'late check-in' arrangements on your or third party website does not mean a thing. They will either abide by it or ignore it. Given that Booking.com do not even have the ETA as a mandatory field, just goes to show whose side they are on.

You are expected to provide a 24hr service just like any other capitol city accommodation provider!

I am not sure how you combat this? Any 'condition' MUST appear on the customers confirmation e-mail to be valid, but if you look at most of them, they do not even provide the terms and condition of your cancellation policy, which I thought by law they had too?

You can prevent 'same day booking' via your Channel Manager to eliminate some of this problem, but that puts you at a disadvantage

What gives me some hope is human nature. I have had three instances of this in three days (we close at 9pm):

The first thought that it was perfectly acceptable to turn up at 10pm without calling us having given a duff phone number. They were growled at and I will probably get a bad review!

The second abode by the rules, phones and was so grateful that he was able to get into his room at 11.30pm.

The third rang at 5.30pm and was so surprised that we answered the phone and were not closed!

Say no more!