Legit or Scam? MXN Conversion Rate for Hotel Bill

We are staying at the Four Points in Mexico City. I always have my credit card charged in the local currency as my understanding is the conversion rate is better. The front desk clerk insists its cheaper if they convert the fee and I do the charge in USD. Does anyone have experience in this and is it true or a scam? FWIW I would probably use my Chase Bonvoy card.