Some of the system warning messages the Vita produces can be a bit confusing, but never fear – you can indeed earn trophies from used games.
As many users have discovered, popping a used or borrowed Vita game card into your new handheld results in a message warning you that no trophies can be earned, and in most games, the previous player’s progress will be carried over.
To correct this, simply choose no when prompted as to whether you wish to use the software. In the system menu, tap and hold the game’s icon to enter rearrange mode, then use the “…” prompt which appears on the game icon. You can then delete the previous user’s data and begin afresh, with the ability to earn trophies. Pocket Gamer has a visual guide for those needing assistance.
Having tested this with several game cards it has become clear that players cannot share games unless they are willing to forego trophies and carry over progress between them – there doesn’t seem to be any way to retain individual save data when reformatting the card to enable trophies.