Buy apps outside Google Play store

I found an App i liked and wanted to buy it, but not through Google play store, so i mailed the developer, and i was able to buy it using paypal. The developer send me the apk after payment. Maybe we can sum the “outside-Playstore-sellers here”:

[root] AirAudio - stream your music ! eu.airaudio

Cool. I have tried the same way with the developer of watch droid, but he can’t give me a paid app, because the app is checking the licence via Google play services :weary: