One auction equals one impression of the ad rendered to a user.
The auctions are completely dynamic and reset every time the page is reloaded, in this way, the number of total impressions that a vendor has is the total number of auctions they have won. However, impressions are not exactly comparable due to market conditions; impressions rely primarily on-page traffic. For example, in summer, it is more likely that on a toy marketplace, the water gun page will have more traffic, therefore more page loads, therefore more impressions than the winter sled page.
You can check manually which vendor has won the current auction by physically checking the marketplace for the product listings marketed as “Sponsored” or shown as a banner ad.
There is no single definition of "best”; some vendors will be performing best on total sales, others on ROAS, etc. Vendors will have different aims and strategies.
Updated 3 months ago