The way I’ve heard it is that it’s not just coincidence nor microphone scanning, but just the effectiveness of targeted ads in general. You could be within wifi range of other users who are searching for pickle stuff or you yourselves have a history of pickle purchases, etc. This stuff is scary specific already.

They are, but likely not passing the savings on.

More options, especially initially, is good. Users will migrate to the better one over time.

If this interests you, consider the book Ultra Processed People.