Myth 1: Everyone speaks some semblance of English
You'll likely be able to get by in major global metropolises, but don't count on a single cab driver, most restaurant staff, or even many hoteliers in Mainland China to have a clue what you're saying. Similarly, there's a romantic notion Stateside that all Europeans are remarkably bi-, tri-, or quad-lingual, but it's not true. Why should the waiter in Avignon speak any more English than your local McDonald's cashier speaks French? The least you can do is carry around a translator; everyone already knows you're a tourist -- own it.
Myth 2: Duty free's a good deal
Unless you're scoring a magnum of Jim Beam and cartons of smokes, duty free isn't really a great deal most of the time. About 1/3 of items purchased are high-end products like bags, sunglasses & jewelry; and even though the items are tax free at the airport, they're often marked up beyond what they'd cost in outside stores. Exception: Countries with steep taxes on booze. Landing in Australia? Stock up before catching your 'roo into the city, where pre-gaming's noticeably more expensive.
Myth 3: Pick-pocketers run rampant
Most destinations where tourism's big are safer than you think. Is there a chance you'll get pick-pocketed on Las Ramblas in Barcelona, or riding the Paris Metro? Of course, but it could also happen in a place like Wilmington, NC, and that's where Dawson's Creek was filmed (mad safe). There are, however, some general rules to follow to ensure your wallet stays where it belongs: DON'T keep it in your back pocket when you're in a crowd, DON'T whip out a map on the street, revealing yourself to be a clueless tourist, and DO wear a wolf t-shirt -- they're badass and no one messes with dudes in wolf shirts. It's a fact.
Myth 4: Your souvenirs were made locally
Unless you're in Honduras or China, chances are those "authentic" goods the vendors are wildly shaking in your face were made elsewhere… like China or Honduras. While most people say they buy said tchotchke as a reminder of their trip, this is BS; you bought it so you can drop it into conversations back home -- admit it.
Charlie: "Hey, is anyone going to Phil's tonight? I heard it's going to be a great party."
Recently-returned-home-from-traveling guy: "I hope no one will think it's weird if I wear my new Thai fisherman's pants and pashmina. Both are wardrobe staples in Southeast Asia."
Charlie: "Who the hell are you?"
Myth: Haggle for everything, and never pay more than 10% of the asking price
The truth is, not everyone's trying to rip you off. And that $7 bag you insist is only worth $6? The buck in-between is way more useful to the vendor if you've got the means to travel abroad. A good question to ask before you start wheeling-and-dealing: Is that bag worth $7 to you, regardless of the knowledge it might be sold to a local for $6? Yes? Sold. No? Move along in search of another bag.
Myth 6: Tours are for suckers
Obviously this can be true, but chances are your tour guide knows a ton of people, a ton of cool bars, and ton of places to score delicious local eats. You're essentially paying for a best friend, but one that won't make out with the girl you like at the bar and then say she wasn't your type anyway -- thanks a lot, Dad! Guided tours also provide you with a way to get exclusive access to cool things, like the Señor Frog's VIP room.