Hello. My name is Michael. I can help you with your question.
One option you have is to use WordPress Multi-site. That will give you multiple sites for clients under a single WordPress installation, but what it gives you are full WordPress sites. That may be more than what you are looking for. If it is, and you are just looking for something to separate the commerce, and leave the site admin under one site, let me know and we can explore your options with that.