LOS ANGELES >> My husband, Joe, and I went to Chicago at Christmas to visit my family. Often, you can fly round-trip from Los Angeles International Airport to O’Hare International Airport for about $250 to $300, but the price goes up by at least a couple of hundred dollars closer to Christmas. We found a $499 fare on United in October and bought tickets.

We could choose our seats on the Chicago-­bound flight and were told that we could select our seats for the return flight up to 24 hours before departure. Both ways were regular economy fares, no zero-frills basic economy on which you can’t have a carry-on and don’t get assigned a seat until you get to the airport.

The flight to Chicago went fine. We paid the standard $30 extra to check one bag, like chumps. But we hit a problem on the return.

We got the text saying it was 24 hours until departure at 5:50 p.m. Saturday. We were at a computer to check in and select our seats at 5:58. When Joe looked at the seat selection screen, only one seat remained in economy. Every other seat was marked “Occupied/Unavailable” or was in Economy Plus or United First, which required hefty upcharges.

My options at this point: Pay even more to guarantee myself a seat on my flight home or show up at the airport and hope I didn’t get bumped. Considering it was the Sunday after Christmas, peak holiday travel time, and I didn’t know how many more flights to LAX were scheduled for that night, I paid the extra for Economy Plus. After taxes, it cost $92.

I did not feel good about this experience. Was there something else I should have done? How could I have gotten out of paying extra but still guaranteed a seat on a flight I had booked more than two months earlier? Why did United sell me a ticket for a seat that didn’t appear to exist?

Charlie Hobart, a spokesman for United Airlines, had some answers for me.

“If a customer does have questions about their seating assignment or lack of seating assignment, they can reach out to us,” Hobart said. Customer service representatives are available 24/7 by phone at 800-864-8331 or on Twitter (@United).

If you find yourself in the same scenario and don’t feel like spending the last day of your vacation on the phone or getting into it on Twitter with an airline customer service person, you can proceed with check-in without selecting a seat. You will be assigned one when you get to the airport.

“Just because you do not have an assigned seat when you look to check in does not necessarily mean that you’re not going to fly on that aircraft or that you’re going to miss the flight,” Hobart said. “What we don’t want a customer to think is, ‘Oh, there are no available seats, so the only way I’m going to get on this flight is for me to purchase an upgrade; it seems like that is my only option.’ That is not what we want customers to think.”

Still, that’s what it felt like. Zach Honig, editor-­at-large at travel blog the Points Guy, doesn’t blame me.

“It makes perfect sense that you would want to pay to select that seat,” he said. “Anyone I know would have made the same decision.”

Honig and United’s Hobart said if I had proceeded with check-in without selecting a seat, there would have been a message reassuring me I would be assigned one at the airport. That message did not appear on the seat selection screen.

As an extremely frequent flyer, Honig is familiar with the ins and outs of the process. But for mere mortals like me, who fly a few times a year but aren’t air travel experts, he said showing up at the airport with no seat assignment can be stressful. Most likely, he guessed I would have been put in one of the unselected Economy Plus seats without having to pay, or someone in regular economy would have been moved up and I would have gotten that seat. I even could have gotten upgraded to first class. But I also would have been running the chance of getting bumped from an oversold flight.

The seat selection screen is “an upsell opportunity, clearly,” Honig said. But it’s not necessarily the airline hiding “free” seats from me in a bid to take more of my money. Upgrades are handed out as boarding time approaches; by having passengers show up without assigned seats, the airline can shuffle the last few stragglers into whatever seats are left.

If you find yourself in my shoes and you’re not willing to pay extra, you can go to the airport and hope for the best. Good luck.