Improve Customer Satisfaction
Since you own the marketplace, you don't have to focus on any of the problems of having physical inventory that we mentioned above. That means you can focus on making every end user—seller and buyer alike—as happy as possible.
Running a marketplace requires entrepreneurs like you to take the reins in creating a platform that meets user needs, typically via the curation of content and moderation of any problems. This is the value that people on both end of the transaction are looking for.
Because you can focus all of your energy on making marketplace users happy instead of running the inventory part of the equation, you simply focus on customers and their satisfaction. That's something that can keep them coming back again and again.