Originally Posted by
ElevatorEnthusiast
As an update, I asked the property at check-out what exchange rate they use. They replied with something close to 21.5. I told them that sounded high. The agent responded that they know but that they never change the exchange rate, which is...a strategy. I didn't push further as it wasn't worth escalating. I just arrived at my next hotel (also Bonvoy) and asked them what exchange rate they use - only USD listed on my check-in sheet. They replied that it was 19 something and that they just changed it, which matches the current 19.7 rate that Google has. So, yes, YMMV between properties on the fairness of the exchange rate.
As another update, I've found the culprit of these inflated exchange rates - Grupo Diestra. They own both the Marriott Reforma and JW Santa Fe in CDMX, and both have forced an inflated 21.8 exchange rate. FWIW, no exchange rate issues occurred at either the W in Polanco or the Westin in Santa Fe. If you look at reviews for other Grupo Diestra hotels elsewhere in Mexico, you can see a few complaints here and there of exchange rate issues.