You will primarily see this through the increase in your impression count. If you are winning auctions, your ad will appear (Sponsored Listing or Banner ad), and more customers will see it, creating higher engagement levels. Of course, this is not always the case, as impressions of your ad rely on traffic through that page. As auctions are refreshed with every page load, the number of impressions is the number of auctions you have won.
You can also check the marketplace website manually to see if your product/ad is listed in the premium spot.