Adsense doesn't make sense to me if I am selling a product or a service. Why take someone off my site for a few cents and onto a competing site when Google is making many times more. After all adsense matches keywords on your site to words advertisers pay Google for clicks. Better to keep them on my site's (and my clients') pages! Now if you are a blogger attracting scores of visitors with the intent of making a few extra cents off someone who doesn't stay there or doesn't link to an affiliate, ad, e-book, etc....makes cents!
No adsense on your shop site, or only on pages after your customer bought something, then you can direct them to a the thank you page with more content and adsense ads.