Im looking for someone to clone the functionality of OutlineDepot.com.
That website allows buyers to create an account and purchase digital products. It also allows sellers to create an account and upload digital products to be sold.
The owner controls the format, presentation, and price of the digital products.
I think some of these themes might work for doing this – https://themeforest.net/category/wordpress/ecommerce?term=digital%20download%20marketplace