Sure, but factor those in and you still end up being able to offer cheaper ticket prices by overselling. It is clear that this is true from existing market behaviour.

> You have 100 seats, you sell 100 tickets. People have to show up to fly with you, no refunds if you don't show up.

That is one way of running an airline. However, given that some proportion of passengers change their plans in practice, overselling will cause a reduction of ticket prices in a competitive environment. This is just textbook economics and I'm not sure how I can explain this concept better to you.

> If this type of calculation does not cover your costs as the airline, you have a bigger problem in general.

The airline industry disagrees with you.

> I find it highly deceptive that somebody is trying to sell me a seat which he has already sold and is now hoping that one buyer does not show up.

You can find it to be whatever you want, but it is legal and not fraud. Wishing it to be fraud doesn't make it so. You could seek to make overselling illegal. If this were to happen then it would be illegal, but still not fraud.