That makes them untrustworthy. I won't touch any fast food any more, but I would stop going completely based on this alone. I don't support criminal behavior. The lack of deterministic fair pricing is criminal behavior.
Non deterministic pricing is going to open them up to lawsuits and defeat anything they make in the interm. There will be diversity shifts that mirror their pricing changes that will easily show prejudice.
Car life is what kills American health. The whole damn country could get nuked off the planet and there'd still be cars driving around as the only viable transit.