Question on business that helps shops sell to customers live

[FloydO]

 I created a business that does QVC style live product demos for e-commerce sites. I know how to charge hourly for my service but I think shop owners would appreciate the option of paying a small hourly rate plus commission on the items sold.

The question is if I sell products for 10 hours a month on someone's Shopify website, how do I know how much product moved on their website during my selling time? What would be the best way for me to ask the Shopify owner to show me the sales and how would I know the information is correct and not made up? Any ideas?