For some flyers, price is the only thing that matters when choosing an airline. This is where travel comparison sites come in handy: When legroom, food quality, and seating assignments aren’t deciding factors, customers can arrange flights by cost and choose the cheapest option available. But as a recent story from The Economist points out, at least one airline has found a way to game the system so that those cheap flights can end up costing more later on.

Delta, United, and American Airlines all offer something called “basic economy" (or “last class,” as it’s more commonly known among flyers). By forfeiting the ability to choose their seats, passengers can snag tickets for cheaper than what they’d find in regular economy. For frugal flyers that may sound like a sweet deal, but United just revealed another condition that may cause some customers to reconsider it. By agreeing to fly in basic economy, passengers lose their privilege to store bags in the overhead bin. The only luggage they’re allowed to bring on board is a carry-on bag small enough to fit beneath the seat in front of them.

Customers who always travel light would likely be happy to have the option to pay less than those who bring on heavier loads that require more fuel. But if you aren’t aware of the bag stipulation beforehand, you could end up losing the money saved on the ticket when it comes time to check your baggage. The Economist suggests that the basic economy price tag may be a sneaky way for United to climb to the top of flight searches on sites like Kayak and Expedia. Customers buy the cheap ticket assuming they’ll have access to the overhead bin. But depending on how many bags need to be checked (United charges $25 for the first and $35 for the second), a regular economy ticket may have been the savvier choice.

United is the only airline to include luggage restrictions in their basic economy offers at this time, but if it proves to be a money-maker for the company, Delta and American could soon follow suit. When selecting a flight, always read the fine print to make sure you’re getting the most for your money. If that $200 flight across the country turns out to be too good to be true, there are other strategies, like shopping in the middle of the week, you can use to score the best deal possible.

[h/t The Economist]