On the contrary, you can build your own platform that may or may not leverage these marketplaces, but the lifeblood of your business depends on your self-hosted website, blog, mailing list, etc.
Building your own platform is great because you own the customer list. You have their emails and their transactions are made fully with you and for your profit, there's no middle man.
However, building your own platfrom costs time and money in its own ways. You have to build from sratch an audience, blog, secure ecommerce platform, etc.
How would you find a middle way? How would you advice an entrepreneur to earn & provide value quickly, while building their own customer list?