how to stop an app upgrading? How can I pin an app so that it can't be upgraded? I have one app where version 2 is not as good or stable as version 1, so I want to pin it at version 1 and not upgrade it .
I needed to do that for Google Maps.  I still believe the original Google Map is about the best.  The upgrade lost a lot of functionality, almost two years ago and still hasn't caught up.

So I had to do the same thing you described and found that the only way to do this was to disable auto updates and only manually update the items (all the items) except for Google maps.

You can disable auto updates by going (from the Android) into Google Play > Apps > Options > Settings > (Click on) Auto-update Apps > (Tick) Do not auto-update apps

After you have done this, you'll be notified when Apps have updates.  You can select which ones to update from the notice.