P.S. Don't be too blatant and it may not always be possible, but ask for a copy of the bill when you check in.

Why? Because you might get Bonvoyed and Marriott's IT won't post your stay automatically. And in Bonvoy's infinitely awful wisdom, you can't request retro-credit without sending in a photo of your hotel bill. It can be a royal pain to request it from the hotel later.

It's one reason why I am loathe to fully mattress run Marriott hotels any more.