Turning to a full-fledged ecommerce platform is not always an option for some organizations, because this can turn out to be too expensive (with monthly payments and all,) and you may already have a website built and you'd rather expand that platform as opposed to transferring everything to a more cookie cutter system like Shopify or Bigcommerce.
Ever since I've started the blog I had this idea in the back of my mind to gather information about *all* existing shopping carts and ecommerce platforms out there and document their journey.
Multi-vendor online shops, aka marketplaces, are gold mines when done right. The big dogs are Etsy and eBay, but you can find popular niche multi-vendor sites such as ThemeForest. The idea behind multi-vendor sites is to allow people, or companies, to create profiles and post their products for sale.
When customers come to your multi-vendor site they can pick one item from John Q web designer and another from Company XYZ and it is all processed through the same shopping cart. The multi-vendor payment processing system divides the payments behind the two vendors and everyone goes home happy. This ecosystem of people creating and selling in one place helps the customer find a more diverse set of products, and you, the site owner can make some big bucks through fees.