Board Thread:Game Discussion/@comment-37377299-20181102032456/@comment-28169398-20181102035452

You need to have Enable Usage Sharing set to Yes so that your game data is populated on their servers under your player ID.

You can find the setting under the ⚙️ and then ℹ️ icons at the bottom left of the game screen.

From there, they can verify if you owned something or not from the data that you shared with them. Screenshots and even videos could be from someone else's device, which is why it is insufficient proof.