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I ran into a problem on my flight from San Jose to Mexico City, which was on Avianca. I knew these were small planes, so I prepaid $33 for each checked bag. But when I checked in at San Jose, the agent had no record of my prepaid bags. I discussed it with them and showed my receipt. I even spoke to a supervisor. But I ended up having to pay $90 per bag.

I have copies of my boarding pass showing “no checked bags� and the receipt for the $180 fee. When we arrived in Oaxaca, I called the phone number on my receipt, but after speaking to a representative, we were disconnected. A representative emailed me and said there should have been no issue with the baggage. She invited me to file a claim. I’ve heard nothing since. Can you help? — Peter Holt, Woodinville, Washington

A: GoToGate is an online travel agency, which means it is supposed to represent your interests (and it also takes a commission from the airline). Even if there wasn’t time to sort out the luggage problem at the airport, the agency should have quickly refunded the extra fee.

Let’s take a step back. Why are airlines charging so much for checked baggage? Because they can. Airlines know that we need to travel with luggage, so they charge for it when we buy our tickets — and if we don’t immediately say “yes,� they more than double the price and charge us extra at the airport.

One day, when enough passengers refuse to play along, airlines will stop this nonsense.

Evidently, your reservation was handled by multiple online agencies, which made your resolution a little more complicated and may have led to the crossed wires.

At some point, you also dealt with a third agency called Mytrip, which is owned by the European online agency Etraveli Group.

How do you avoid something like this? Book directly with the airline, because going through intermediaries just leads to confusion and potential problems.

I contacted Etraveli Group on your behalf. A representative contacted you and refunded the $180.