It’s easy to make mistakes when you book your own travel arrangements. Corrections can be costly.

A few years ago, I was arranging for our family of four to fly to Montreal. I made online reservations with WestJet, which confused me by referring to passengers as guests.

When asked how many guests were travelling, I said three (thinking I was booking flights for me and my guests). This led to an expensive rebooking for four of us on a later flight.

Here’s a cautionary tale about a customer I’ll call Rachel. While booking flights at online travel agent Travelocity, she mistakenly put in Jan. 15, 2015, as both the arrival and departure date.

The first flight left Toronto at 6:29 a.m., with a stop in Philadelphia, arriving in San Juan, Puerto Rico, at 2:30 p.m. The second flight left San Juan at 4:50 p.m., with a stop in Miami, arriving in Toronto at 10:59 p.m.

It seemed absurd to make a round trip of 6,737 kilometres in order to spend two hours and 20 minutes in San Juan. Even if you wanted to do that, you would have no cushion for flight delays.

Rachel called Travelocity the next morning to explain her mistake. Travelocity called the airline, which said she had to pay at least $500 for two people — on top of the original $450 apiece — to rebook the flights.

“I should not have been able to make this humongous mistake,” she said. “Travelocity’s software should have alerted me before I confirmed everything. There should be a grace period.”

There’s no grace period when booking airfares. Once you pay for a ticket, you own it. Changing dates and times will cost you extra money.

Still, I thought Travelocity might have caught the problem by checking with Rachel when she made the booking. Did she really plan to take such a long trip in a single day?

“This was a customer booking error,” said Travelocity spokesman Sean Citrigno, adding that there were several opportunities to check the details during the booking process.

“While this particular trip (Toronto to San Juan) may have been odd for a day in, day out venture, the site does attract plenty of business travellers who book day travel and, therefore, does not flag such bookings.

“Since Travelocity.ca is merely a conduit to the sale of the trip, there is nothing to do about the additional flight fees. These are dictated by the airline.”

He offered a $100 credit to help recoup some of the cost. But Rachel felt she could not afford to rebook the trip.

Rob Woodman had a similar problem. He booked three return Air Canada flights from Toronto to Orlando, Fla., with Expedia, but mixed up the dates he wanted (March 14 to 22, 2014) with the same dates in February.

“I probably would not have made this mistake, except that the 14th of each month fell on a Friday,” he said.

He noticed his error two weeks later when booking a car rental. Expedia said the tickets were non-refundable, but he could use them as a credit toward flights on the correct March dates.

“This is where it gets frustrating,” he said. “I paid $1,600 each for the February tickets, but the equivalent dates in March were only $700 each. I would lose the $900 difference and it would cost another $200 to make the change.”

He decided to pay for the March flights and save the credits for a later trip. Then he learned that each credit included $168 in taxes that he couldn’t claim.

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Expedia said it would ask Air Canada to give a refund of the unused taxes. It would also offer a future travel credit as a goodwill gesture for his inconvenience.

Booking travel online leads to complications if you are not careful. Using a travel agent can reduce the chances of being stuck with arrangements you can’t use.