Its like everywhere else, people are always tries to scam you if you are not very careful. I saw many tourist due to language barriers and culture miss-understanding,they are get scamed. And yes everyone has to be very careful with the locals specially in small areas.

I never had a problem.

My fiancé is Brazilian and we often fly to Rio because of his business. of course you have to always pay attention and not show off very expensive stuff, but can be a pretty nice place to go to.

Where ever you go, you should'nt show off expensive stuff. That's a golden rule for any trip you do, to a new country or place.

I really do not think that Rio de Janeiro is unsafe, it all depends on where you stay and the places to visit, if you do not go out of the turist circuit, it will be ok