The problem is that Google offers a recommendation which the searcher can't evaluate until later. This is especially true with ads. Google recommends a business to me (by showing me an ad) but Google doesn't know if the business was good to me. I don't even know if the business was good to me until after I received the service.

Ideally, I would buy through a Google service (Checkout) and then Google would provide me opportunities to rate the business after the sale. These ratings could affect an ad's quality score. Done right, this would allow Google to introduce me to the businesses most likely to satisfy me. Google would become more of a trusted advisor to searchers rather than just another advertising company.