Mac App Store - how to check which account was used to buy app

Solution 1:

All app downloaded from Mac AppStore(MAS) contain a receipt inside their app bundle (example: appname.app/Contents/_MASReceipt/receipt). MAS will scan this file to check whether the new version is available.

You can use this application (Find Any File) to search any receipt on your drive: http://apps.tempel.org/FindAnyFile/

1. Launch 'Find Any File' and search for: _MASReceipt
2. Go through each result that you think could be the culprit, copy the receipt to your desktop as a backup, and after that delete the receipt inside _MASReceipt folder.
3. Open MAS and let it scan for software update. If it's still showing the wrong ID, it means that you've deleted the wrong receipt. Restore the receipt backup from your desktop to it's previous location.
4. Repeat the process until you've found the problem receipt.

Solution 2:

To make the AppStore forget the old credentials with which an app was downloaded, you must remove the _MASReceipt directory in the app itself.

To do this:

1. Open Finder and navigate to Applications,
2. Ctrl+Click the application you want to redownload and choose "Show Package Contents",
3. Expand the Contents directory and click _MASReceipt to select it,
4. Type Command+Delete to delete the directory permanently---you will be prompted for your credentials since this is a protected file.

Quit and restart AppStore, then find the application you want to update. The button should now say "Free" or "Install" instead of "Update". Clicking it will update your app to the latest version, doing so as the currently logged-in Apple user.