We booked one week in advance a 5 star hotel (Hyatt Regency Grand Reserve) in Puerto Rico for a very reasonable price. We booked a King bed with a garden view, but upon arrival got a little downgraded king-bed room. After showing at the reception what kind of room we booked, they had no problem changing it for us a few moments later.
Long story short, we got a very good deal, but also because the hotel staff was very nice and helpful.
Also, we weren't charged anything extra upon arrival.