Unfortunately, Rio de Janeiro is a slaughterhouse for tourists. I'm Brazilian, and even that didn't stop taxi drivers and the like from trying to outsmart me. Nothing serious, but that sheds some light on what foreign tourists should expect. Cariocas can be incredibly difficult people to deal with. The malandro culture of which they are still proud gives them a bad name all over the country, and they deserve every bit of it.

Here are some additional hints:

  • It's very likely you'll use taxis a lot. Public transportation is unreliable and dangerous. All taxis have working taximeters (small machines that control your fare) in front of the passenger seat. Don't enter a taxi that doesn't have one, they are illegal and for all you know the driver could be, and probably is, a criminal. There are no exceptions.
  • You only have to pay what the taximeter says. There are no extra charges, no extra percentages, no taxes, no anything. Rounding up to the next real is usual, but you don't have to do that.
  • Always carry change to avoid trouble. When I was there every single taxi driver claimed they didn't have change. That's a cretin attempt to make you pay something like R$10 for a R$6 run. Just for comparison, in my city when a taxi driver doesn't have change he rounds the fare down until he does, and several times I was given free rides because the driver didn't have change. You won't see this kind of friendliness and decency in Rio, but you don't have to pay more than what the taximeter says. If you want to be political, go with the driver to a nearby shop and buy something small like a candy in order to get change. On the other hand, expecting change for R$50 without mentioning that before the ride is rude in any city.
  • Carry a map and track the path. It'd be better if you could ask a local which is the shortest safe path to your destination and ask the driver to follow it.
  • See those favelas? Poverty is not picturesque. Stay away from them. Some companies will offer programmed visits to safe, tourist-friendly sectors of the favelas. Don't even think about going there alone. I assure you well over 99% of the people living there are hard-working, honest people, but the remaining 1% are real, dangerous criminals. The worse parts of those favelas are run not by the government, but by criminals. They run a separate State there. You are not invited.
  • Watch your pockets, don't walk around with fancy cameras, jewelry or "hello, I'm a tourist" Hawaiian T-shirts. If you are too white that can be almost impossible to conceal.
  • If you got R$100 bills it's unlikely you'll actually be able to use them, much like the US$100 bill. Even R$50 may give you a hard time. It's a good idea to take a good look at the money you get from trusted sources (like a bank) in order to avoid counterfeits. Except for an experimental plastic R$10 bill, all others look alike, with the Republic on the front and some animal on the back. Brazilian money has very strong security features which are very easy to check if you know what to look for. Counterfeits are not common, but it's more likely that they will be found in a touristic city, and it's more likely that people will attempt to cheat you because you are a foreigner unfamiliar with the money, so beware.
  • In case you are in trouble, call the police, a friend, or your hotel if you are not sure. The police is not very reliable, and they may be corrupt, but there's not much else you can do.
  • Brazilians usually don't know any foreign languages. You may use Spanish if you know it, but speak slowly. Portuguese and Spanish are sister languages, but unless you are a native Spanish speaker speaking in a calm tone you'll have a bad time, so be patient. As a rule of thumb, if you are not being understood, you are the idiot with a communication problem, not the person you are talking to. I've seen natives doing their best to help tourists speaking in languages less closely related like Italian or French. Brazilians are eager to understand and to be understood. Pour in a few Portuguese words that you learn during your trip and you will make friends. However, treat Brazilians as Spanish speakers or as inferiors because they don't know your language and you will deservedly make enemies. This is particularly valid for American tourists.

Of course, the above mentions only the bad parts. Personally, I've enjoyed my trip to Rio, even though it's far from being my preferred place. I watched a public MPB show in a square in Copacabana, visited stunning places and met friendly people. But the carioca willingness to rip you off is a great disturbance that can ruin your trip. As always, YMMV. Good luck.