I have an app that I want to connect to my web site via login in the app. Once logged in, the user can purchase extra content. So, I'll open the browser on the device and let them choose from choices on my website. Upon purchase, sending them to Paypal for example, what's the easiest way from the app's perspective to determine that the sale went thru and it's ok to download the content? Is there a "common" way to do it? I was trying to stay away from in-app billing. I've seen other apps do it the way I describe.
Have a look at in-app billing and there is also a nice tutorial here. You probably won't be able to use paypal.