This site exists only because of the airline's outright hostility toward its passengers and many of its employees.
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First, don't expect United Airlines to respect your rights. As Daniel Bernstein notes in his insightful analysis, it doesn't make economic sense for United to obey the laws. United assumes that most passengers won't go to the trouble of making a written demand for payment, and following up on it (e.g., through small claims action or notifying their attorney-general). This way, United can can save a lot of money by ignoring its legal obligations.
The following offer some guidance in how to make sure that United takes your complaint seriously, and that you obtain the compensation you are owed.
Credit to Gábor Lukács, a Halifax mathematician and air passenger rights advocate, for much of the content in this guide, which appeared originally on the CBC Marketplace blog. Follow Gábor on Twitter: @AirPassRightsCA