Running an airline is a surprisingly unprofitable business, considering that the model does revolve around charging people many hundreds of dollars to sit in a chair. But as the WSJ points out, airlines have a creative new way to charge you a hundred bucks for something that used to be called “common courtesy.”

The Journal details how airlines have leeched on to the “family fee” as a new way of charging for flights. It used to be that when you booked four tickets at once — say, because you’re a perfectly normal family going on holiday — the airline would book the four of you in seats next to each other.

But this is a brave new world, and airlines running on razor-thin profit margins must grasp onto every possible chance for cold hard cash:

A few carriers are openly marketing the so-called family fee. Frontier Airlines, which since 2014 has charged for all advance seat assignments, has a drawing of two people with a child on its website saying paying is recommended to “keep your party together.”

Parents face the choice of adding fees on top of fares or begging other travelers on packed flights to switch seats so children aren’t sitting alone with strangers. Often when there are seats available that don’t require fees, they are all middle seats that would space family members one behind the other rather than side-by-side.

This follows a disturbing decade-long trend of airlines inventing new fees where there were none before. Remember when you could snag extra legroom by stealthily booking the exit-row seats? Now, it will cost you a cool $49 to do so. Baggage fees are notorious, but some budget airlines will now charge you if you don’t check-in online.

Some of the details outlined by the WSJ highlight how depraved the reservation fees are. It’s one thing for airlines to charge extra for seats with more legroom, or even for seats further up the cabin.

But it’s a whole new level of trickery when airlines use online seating maps to make the plane seem full, pressurizing you to pay a fee to reserve a seat, when the plane’s actually half-empty:

Louis Silfin, a banking consultant in New York, was traveling alone recently when he decided to pay $9 extra to move closer to the front of the plane on what appeared to be full Delta flights from New York to Boston and back. When he boarded each time, his row and the one behind him had only five people filling 12 seats.

“Why did I just pay for a better seat when I could have just moved around anyway?” Mr. Silfin asks. “What was on the airplane was definitely not what was on the seat map.”

Happy capitalism, everyone.

Chris Mills has loved tinkering with technology ever since he worked out how to defeat the parental controls on his parents' internet. He's blogged his way through Apple events and SpaceX launches ever since, and still keeps a bizarre fondness for the Palm Pre.