By 'marketplace' type website, I mean sites like Amazon or Lazada where multiple users can register as either a customer or a seller and also the site should handle displaying products from those sellers as well as inventory through a CMS.
I have been thinking about building one and I pretty much gotten everything I mentioned above down but I'm not too sure if I know PHP and MySQL well enough to build a secure website of this type. I am paranoid someone would hack it or something.
So, for anyone who has had experience in building such systems. Care to share what problems or challenges you faced in building sites such as these?