Shopify stores owners have an admin page which shows them how many customers have purchased and how many have abandoned their purchase. (See the screenshot example below.)
You can’t see that page but, because the link has the same format for all Shopify stores, you can create the link for any store owner. Send the link to Shopify clients and let them see how many sales you can recover for them.
Here’s the link format. Just replace “[Shopify Store Domain]” with the store’s domain.
https://[Shopify Store Domain]/admin/checkouts