Boost your Ecommerce store with Vertical Ecommerce store aggregator

What is a Vertical ecommerce store aggregator ?
An ecommerce website that connects to multiple ecommerce stores like Shopify, Amazon, Wix, WooCommerce etc.

I am building a ecommerce website to gather multiple vertical ecommerce store vendors in one location.

Please see my landing page
https://www.servicefolder.com/listing-apps/hvac-ecommerce.html

Questions:
How do I know there is a product-market fit?
How do I reach out to the respective vertical vendors?
Is there a value proposition to the vendors to take subscription in my website?
Are there similar aggregators for other domains?