Daryl Preston and his wife are flying from San Francisco to Rome this summer, and they have tickets on Lufthansa. Four tickets, to be exact.

“We’re double-booked,” says Preston, a retired physics professor. “The names, method of payment, departures dates, return dates, and the flight numbers on the two bookings are identical. Copies of the tickets are attached.”

No copies were attached.

How did the Prestons end up with four tickets instead of two?

Well, at my request Accent On Travel, a travel agency, made the first booking on January 2, 2012. On January 7, I made the second booking via Expedia.

Why did I do such a thing? Well, I am 73 years old and my short term memory is not as good as it used to be and I had forgotten the first booking. In addition, Accent On Travel did not notify me of their booking until February 1.

The double booking was an honest mistake.

Preston wonders how two reservations can be made in the same name, considering the sophistication of the reservations systems and the state of airline security. That’s a valid question.

Lufthansa is willing to offer the Prestons credit for a future international flight after a $500 rebooking fee.

“I seriously doubt that we will make another international flight,” he says.

Preston wants me to ask Expedia to refund the Lufthansa tickets. I’d like to help him, but I’m not sure if Expedia is the right place to start — or even if I would be successful at fixing this.

Double-booking cases fall into two general categories: those created by the website, and those caused by human error. The technical ones are usually easy to take care of, but not always. Here’s a rare triple-booking case that took a whole year to resolve.

When it comes to mistakes made by people, airlines and online travel agencies can be considerably less forgiving. But again, there are exceptions. Here’s a case with similarities to Preston’s, except that the double-booking was made by a 17-year-old who was confused. Delta refunded the money, even though a majority of voters said I should stay away from the case.

Incidents like these make me wonder if too many people are trying to book their travel online. Whether you’re 17 and just confused or 73 and forgetful, it seems you should be staying away from the PC if you think you might make a purchase you’d regret. And if you can’t do it, then maybe there’s someone in your life who should either restrict or supervise you when you’re surfing the Internet.

Let me be clear: I’m not saying Preston needs a babysitter when he’s on the computer. He’s obviously a brilliant guy. But if he’d simply decided on Jan. 1 that he’d shift all of his travel to the bricks-and-mortar agency and deleted or disabled his Expedia account, then this wouldn’t have happened.

I think if anyone’s going to refund the second ticket, it’ll be Lufthansa. But should I take this case, even though technically, Preston is responsible for both reservations?