You are right, but companies can take on the attributes of monopolies once they have your money.
GMAC is one example, another:

Mexicana airlines is apparently in trouble again, something we didn't know before buying tickets from Merida to Villahermosa last week. At the time everyone was boarding the flight, the agent announced that no one's luggage would be making the flight; it would be sent separately on the next flight. Reason given: An outright and ridiculous lie "the aircraft was too small to carry luggage." Several other unlikely reasons have been offered since, but the real reason, I suspect, is that they had a large cargo opportunity and decided to take both passenger and cargo money and dump the luggage. Now we are over an hours drive from the airport in Villahermosa. Our luggage was sent on the next flight alright, which went to Mexico City of course. End result, we had to make a special trip to the airport in Villahermosa the next day to retrieve the luggage.

Not the end of the insults. Turns out our non-stop flight return flight to Merida was cancelled and we were rebooked, without our knowledge or consent, on a flight that first went to Mexico City, then change planes for Merida.  Too much risk in my opinion, given Mexicana's recent behavior. Next problem.  My wife tries to change the flight to a another non stop to Merida. Mexicana now feels they are entitled to a change fee but they can't accept a foreign credit card (for $100 dollars!) and put her on hold to get an international agent who can accept it. She waits 30 minutes and hangs up. More useless phone calls ensue. End result - we're taking the bus. Score: Mexicana - 2 + change, us - 0 minus two one way tickets and lots of annoyance. Recourse, likely none. Best solution, just forget about it. I'm sure you know the expression:    "Ni modo", but for those who don't.

I can swear there ain't no heaven but I pray there ain't no hell. _ Blood Sweat & Tears

When GM sells you a car nobody forces you to go to official GM technical service for repairs: there's always your local mechanic.

Allowing tinkering? Obviously they failed to protect their intellectual property.

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