What if the advertiser's product or service is objectively (according to either a prompt defined by the user or by the UI operator, transparently provided) the answer to the query?
Then the response will also contain ads for things that are not the answer to the query. This is how search engines currently behave.
Example from my work. Many of our customers will search for our company name in order to find the login page. I've watched them do this over screen share.
When they do that, the top search result is an ad slot. The second search result is our login page.
We buy ads against out own company name so that we can be the ad slot as well as the first result. Otherwise a competitor who buys ads against our company name could be the top slot.
Or a phisher could buy the ad slot or game the search results to publish a fake login page to phish credentials. This is why 2FA is not really optional anymore for anything of value.
Example from my work. Many of our customers will search for our company name in order to find the login page. I've watched them do this over screen share.
When they do that, the top search result is an ad slot. The second search result is our login page.
We buy ads against out own company name so that we can be the ad slot as well as the first result. Otherwise a competitor who buys ads against our company name could be the top slot.