How would I know if an asset/package I bought in the asset store has already been used in a commercially released project/game?

If I wanted to release a game commercially or for free. What steps would I have to take to verify that I do not release my game with the same assets that have been commercially released in another game?

You can’t. Some games or assets share if it is used or not but other than that you just cant know.

Unless you recognize the asset / behaviour or do reverse engineering.