The practice of one airline selling seats on another carrier’s planes with its own flight numbers has been around for years, and many travelers are familiar with the term “code-sharing.” Yet even experienced fliers continue to be surprised by what amounts to false advertising.

It’s holiday time, and I’d love to write columns about how seamless and hassle-free travel is — which is true for me in most cases — but I keep hearing from readers about questionable airline behavior. In the latest example, LACSA, Costa Rica’s national airline, may have misled some customers…