How do i know that this platform is secured to list our app?

forceXchange team takes care of your app. forceXchange knows that your app on forceXchange is your hard work and you should get benefits out of it. No one can install your app without purchase whether you are posting it as an open-source(unmanaged package) or as a managed package. You as a Seller can also easily track your app's installation. Salesforce provides you a notification whenever your manage or unmanaged package installed by anyone.