This type of e-commerce platform is a very convenient option, and as such makes it quite popular with a lot of people. The big problem is that most simply rely on the SEO these types of suppliers provide to do the marketing job for them and drive traffic straight to the door. This unfortunately is rarely ever enough to do the job effectively.
Marketing these types of e-commerce platforms is every bit as important as marketing any other type of platform. You really do still need to put your own marketing strategy into play to drive traffic. Simply relying on their marketing strategies to product sales is usually a recipe for disaster. You end up in a cycle of paying the monthly fees for zero sales.