You are trying to solve a real-world problem experienced by a lot of profitable companies, so there is already a market of paying customers waiting for this. One of my clients is actively trying to reduce their dependence on Amazon and instead integrate with other marketplaces.

I see it's just Shopify-to-Shopify for now - bravo for starting with probably one of the most costly integrations. I'm working with a client right now who had to build these integrations using a low-code drag-n-drop platform which allows a quick MVP but has slow job processing, so isn't great for high order volume.

The "amazon" comparison is good for marketing - sure you're not doing all their marketing, or having their reach but you are connecting suppliers, buyers and fulfilment which is a genuine problem.

The companies who would use this often have developers on board already, so providing open source, accepting contributions and turning this into a useful dev-friendly service will almost certainly find paying customers.

Following :)