They are customers of google search in that they buy search results in exchange for screen real estate and suppliers for the reasons you stated above. Google cares deeply about satisfying their search customers because they are also the suppliers of page impressions and personal information.
>For most customers, the product is search results, and their payment is to let part of their screen be occupied by ads.
Would you say adblockers are theft?
Is every consenting value exchange a customer-provider relationship?
>the ideal of such a relationship assumes perfect balance -- two people with things worthless to themselves, but valuable to the other.
Not worthless, just worth less. If I buy a product/service, I felt my money had less worth than what I was buying and the provider held the opposite stance.
Why must it be one or the other?