Have had this in my back pocket for a while. I just checked to see if it still works and sure enough…it does. You can see I tore deep into the SP App Store design with this 4 year old post. What I didn’t show was how one can get the app packages for free and by pass paying for the apps.
This only works with Apps that have a “trial”. Ones that you have to pay for will not be open to this hack as you would have to buy them first. But technically once you have bought it, you can use this same hack to then go post their app package on the internet.
How does it work you ask? If you read through the steps of the post referenced above, one of the back end abstracted parts is to download the app package such that it can be deployed to the target web. The app package will not be put into the database and is required to be downloaded each and every time you request it. In the App Mgmt database you will find the RawXMLEntitlementToken.
This is generated when you click through the Microsoft billing portion of the app install. All apps (Free, Trial, Paid) have to run through this in order to get the token. Once you have this token, you can use it to download the app package by simply pasting this into your browser window:
This will download the .cab file for the target app. Once you have this, you don’t need to pay for the App when the trial expires. Just install it to your app catalog or directly into the site.