Research before you go
Don’t go in blind -- get a better sense of prices, deals, and free attractions before you arrive. Read blogs, follow locals on Twitter, and don’t be afraid to ask questions of the Peruvian coworker who works in accounting (assuming you're traveling to Peru). Some good resources for learning about your destination are BootsnAll, Nomadic Matt, Travelfish, Rick Steves, and Lonely Planet. Remember, when you go in prepared, you reduce the likelihood of getting scammed or overpaying.