We technically got an upgrade at the BWV a few years ago. I booked a SV 1 bedroom. When we arrived, the CM had upgraded us to a Pool/Garden 1 bedroom.
I wasn't very happy about it, to tell the truth. CM offered to put it back to SV but the Pool/Garden room was ready and my DH wanted to watch some dumb football game so we took it. The room was fine. I wasn't rude or mean, but I think the CM was disappointed that I wasn't excited to get the upgrade. Don't know why we got an upgrade.
When I got back home, I noticed our account was messed up due to the upgrade. MS fixed it and all ended well, but I am now very leery of CMs offering upgrades and changes at check in.