“in terms of their own realities and their own situation.” is a huge caveat. Essentially plenty of customers behave irrationally – by any sensible definition of rational. I agree, to make them customers and keep them as customers you need to develop theories that can make sense of their behavior. And it doesn’t make sense to think if they behave irrationally that means randomly (chaotically, unpredictably, uncontrollably). Customers can be predictably irrational (as a group).
Seeing that people will chose* to fly lousy airlines because the initial price quoted is a little bit cheaper than an alternative (or because they are in a frequent flyer program) you can say the customer is behaving rationally if you want. Coming up with some convoluted way to make their decision, which based based solely on their desired outcomes (and cost factors etc.) is not rational, to be seen as rational seems like a bad idea to me. Instead figure out the models for how they fail to behave rationally.
They consistently chose an option they shouldn’t rationally want; in order to save some amount of money they don’t care about nearly as much as the pain they will experience. And the amount they will then complain about having to suffer because they chose to deal with the badly run airline. That isn’t rational. It is a common choice though.
The problem is not in thinking the customers are being irrational for not buying what you are selling. The problem is in thinking the customers will behave rationally. Your theory should not expect rational behavior.
There are plenty of other examples where customers make irrational decisions. I don’t think calling them rational (within the irrationality of their “own realities” makes sense). People will buy things because they think it is a better bargain to get the more expensive item that is the same, for more money, because originally the store charged more and now it is on sale. Anchoring isn’t an understanding of how people are rational. It is an understanding of how psychology influences people in ways that are not rational.