I rented from Europcar in Los Cabos back in November, and have a warning for FTers to avoid any Europcar location in Mexico.

Basically the "scam" they run is that your reservation is booked on Europcar.com in USD, but is converted to Pesos upon return using an inflated exchange rate (in my case, 11.7 Pesos/Dollar). What this meant is that the charge came through on my Amex 10% higher than the original quote, because of the inflated exchange rate from Europcar, and Amex's 2% fx spread.

When I returned home, I called Europcar customer service to complain. Note that Europcar customer service is in Europe (I think Ireland based on the accents), so be prepare to call during European hours. Also prepare to be snapped at, and have calls returned to you in the middle of the night if at all. I was lectured about how "exchange rates change" and that the Mexico location "uses the exchange rate from the bank", which was all nonsense because the exchange rate was inflated.

After several calls, they agreed to a "goodwill credit" of 20 British Pounds. Of course since this comes through Amex, I lose 2%, but it basically makes me whole. But what irked me about the process was the rude customer service staff in Ireland who insisted I was wrong, and only ended up giving me a refund to stop me from calling back.

Use a reputable agency like Avis or Hertz. Even if the local franchisee plays games, you at least fall back on empathetic, competent customer service staff in the States.