Check out how the foreign exchange market works in Brazil

The foreign exchange market is regulated in Brazil and the system is decentralized unlike what you have in some countries where you have the black market controlling the economy of the country and in most cases bringing the country down.

In Brazil, the rate you see online is the same thing you would get when you go to the fx office to change or buy dollars or any other foreign currency you want. They would take their own tax and that's it, different from what you have in Nigeria where it is so difficult to buy foreign currencies and then you have no choice but to buy from the black market, pure madness, a country must not be allowed to function that way.