When a merchant creates a product in the Marketplace app, it will automatically have a tag assigned to it with the merchant's display name, much like how it also gets a tag with the Category Group-Category. So for example, let's say my merchant display name is "Jay at Bold", any products I create would have the "Jay-at-Bold" tag attached to it!
Once you have products ready, all you'll need to do is create a new collection that looks for the "Jay-at-Bold" tag, and it will create a collection that includes all of those products that have that tag.
Easy as that!
If you'd rather see a video of how this works, we'll be uploading one soon that will walk you through this process.