An obvious way is to require some sort of deliberate indication that the user wants shopping results, like a separate pane, or a prefix to the search term. It's a problem largely because it's searching Amazon even when you're just looking for a file on your computer.

Prefix would be good. I guess the Unity way is different keyboard shortcuts (it is possible to limit the search to certain categories). But I won't be able to memorize those.

hold down the Super key for a list of available shortcuts.