huh
You were in a foreign country the bill is due in local currency. The franchisee is under no obligation to accept a foreign currency. (The US dollar is a foreign currency in Brazil). You could of paid with a credit card and not have paid the 5% to the company. Even in the US when someone comes from Canada most the stores never give full rate exchange to hedge against fluctuations. When you travel to Canada and stop at the border at the currency exchange they never give the full exchange they take a little for their trouble. This is called business.
They informed you of the requirement to return the car clean before you left.
If they were trying to rip you off they would have kept their mouth shut and charged you on return.
At anytime you were free to not continue with the transaction but you chose to go ahead. Now you complain here. Did you even bother to contact Thrifty or did you just rant here?