“Sorry. I just had to buy this tequila at the duty-free,” my seatmate on the Mazatlan to Los Angeles flight told me as she crammed her big box next to my computer under the seatback in front of us. “Hope that’s not something delicate,” she added, whonking on her package with her feet to force it in.

To save my computer, I pulled it out and stashed it next to me, thereby violating Federal Aviation Administration regulations. To save money, she should have bought tequila at her neighborhood liquor store. She had fallen for the oldest and most prevalent hoax in the travel business these days, so-called “duty-free store” shopping. There is no such thing.

The United States has granted duty-free preferential trade status to some countries, such as the Maldives, Singapore and, yes, Mexico. But you need not buy anything from those countries in a “duty-free” store to claim the exemption, and most travelers have no need for such an exemption anyhow. In general, U.S. residents are able to claim a duty exemption for $800 in goods. Period. No matter what store in what country you bought it in.

But that’s far from the only entry in a list I call travel hoaxes, myths and scams. To wit:

“Duty-free” stores: There is no store on Earth where travelers can buy goods and be excused from paying import duties when they arrive at their home country. Why would U.S. customs officials give you a pass because you bought a case of scotch in a “special” store at a London airport? Dream on, pilgrim.

These stores are excused from charging customers local taxes, but their prices are often no cheaper. Suppose you decide to fork over $59 for a bottle of Johnnie Walker Black in the duty-free in London’s Heathrow Airport on your way to Seattle? You would have owed U.S. customs nothing — U.S. citizens can bring home that one liter of liquor without paying import duties — and you can buy that same bottle at a local liquor store in Washington state for $50. Yikes: You just donated $9 to the London duty-free company.

The Heathrow duty-free clerks won’t charge you Washington state taxes. And in rare cases, the local-tax dodge does save money; I once saw Kahlua on sale at a Mexico duty-free for $2 less than at my neighborhood liquor store. Why would you and your spouse want to cart a half-gallon (4.1 pounds) of booze through airports and on planes to save $4?

Extra legroom: Sure, 3 to 5 inches of extra space between you and the seatback in front of you seems alluring. But the prices airlines are charging for such extras these days are amazing: $63 on a United flight from San Francisco to Washington, D.C., for example — for a middle seat. The truth is, these days seats have been set to recline very little, including the one in front of you. The real problem is the seat width, which is immutable unless you upgrade. Otherwise, you may have 3 extra inches for your toes, but your ears will still be pinned between two sumo wrestlers.

Flight status updates: Repeat after me: Airlines do not tell the truth about on-time flight status. They want passengers there, sitting in the gate area, in case archangels intervene and their hour-late plane makes up time in a special space-time warp. I have stored on my laptop an American Airlines status page that shows my plane departing Traverse City, Mich., an hour before it arrives at Traverse City. See what I mean about space-time warps? Capt. James T. Kirk must have been scheduled to fly that plane.