[woobar]

There is no ambiguity there. You will get an economy seat or better. If non-premium seats available you will have an option to select one for free. If not, they will assign a premium economy or a comfort+ seat at the time of check-in. If the flight is overbooked having a preselected seat does not guarantee you won't be bumped.

This is something I've observed with different airlines. Google's line "Free seat selection" doesn't guarantee availability of seats to choose from, just that you won't be charged for selecting one if available for your fare.

[hanzmanner]

Delta tells me that there is a seat available at this price before I agree to it. After I agree to it it tells me that there is no seat available at this price unless I pay more.

The agreed upon "seat" in this context includes the selection. This is what this specific dark pattern is about. They are misrepresenting the value of their offering. I want to be able to reserve a seat on my flight. Not to reserve a promise that they will assign a seat... if available, obviously. If not I can just book the next flight and wait for a couple of hours at the ariport. Perfect.