A partnership between Printseekers and a print shop owner is based on a business model called print on demand dropshipping. It works like this:
You have products listed for sale online, for example, a poster with your custom design. Usually sellers have a shop (Shopify, Etsy, etc.), however, other options are possible, such as selling on Instagram;
A customer buys the poster from you, and you get revenue;
Printseekers receive the order information, then produce and send the poster to your customer;
The name "Printseekers" isn't written anywhere, package only has your shop name on it;
You pay to Printseekers for the poster and its shipping, the remaining revenue is your profit.