If all the airlines (or whatever business) are doing something like this, how would you know what the prices are and what the alternatives are? Custom prices per user based on willingness to pay shifts market value around a lot.

> If all the airlines (or whatever business) are doing something like this

Then that would be the main issue and far worse then the algorithms, that's a monopoly or cartel and not a free market. Because in a competitive market prices will be competitive with very little arbitrage.