Well, on a good search engine, IMO, you'd have a predicted store based on the manufacturer (eg their preferred seller) then perhaps a list of top 10 competitors and something like "most recorded purchases after this search are from seller X" with "the most popular similar store is seller Y".
Of course Google wouldn't give that data out as then many companies wouldn't need to advertise at all to get top billing.
That's secondary & the reason Google doesn't have this is likely because the sellers don't want to provide this. E.g. Amazon doesn't want potential customers being easily redirected to Walmart purchases. One of the many reasons Froogle died.
The simple solution is that your paid advertisements are free if it gets clicked when you're the top result anyway. That way it doesn't cost the brand any money to bid on advertisements for their own brand.
Of course Google wouldn't give that data out as then many companies wouldn't need to advertise at all to get top billing.