Originally Posted by craigthemif

In practice you ask the concierge for a reliable "blue" market - take crisp new $100 bills - and you get a backpack full of pesos.

On check out you pay in stacks of pesos - converted at the official rate - but you do pay VAT.

FWIW the government is introducing a new FX rates for tourists paying on their cards - I'm not sure how close it will be to the blue rate - because the government wants more US dollars in the hands of the central bank instead of circulating in the black market. Between that, the VAT and security issues, it might not be worth the trip to buy blue...