pinniped

The discussion of a "downgrade" also makes me wonder if the OP had booked a suite to begin with. Since hotels have fewer of these, I can see where the 3PM checkin/4PM checkout issue might occur with nontrivial frequency. (And no, I don't have a really good solution for the issue...other than to allow the arriving guest to take a downgraded room for 2-3 hours if they want to get in right away, take a shower, etc.)

My own experiences, having booked a non-suite, usually entail waiting for an upgrade vs. just taking some other random room in the hotel. The FD has a lot more to work with in that case...if I'm traveling solo, the random room is usually okay.