I was ripped pretty good by one of the street guys two trips ago. He was offering 90 vs. 81 or so; he "counted it" in front of me, but when I counted it again at my hotel I was like...1500 short...or around $20 US down the drain. Of course, he was long gone by then, I didn't bother going back.
I had always used the proper cambio...but a friend had suggested doing this to get a better rate...never again. For my greed (getting 9 extra Ja per dollar would have netted me about $12 more) I lost $20.
Brasi = dumb tourist that time.