Legality using free Assets from other websites

I found some free assets on some other website (I will not list it here so there are no advertising issues) and I was wondering about their legality. They do not state in any way if they are pirated or simply free anyhow so I was wondering how can one check or know if the assets they use in a game are legal of use and they have no issues after releasing the game? I mean when my game is finished I don’t mind paying for an asset if a situation arises that I was not aware of at first but if my game is released and then I get sued, that becomes a much more serious issue

Unity Asset Store vendors will know if you have purchased their asset or not. If they see a game which appears to use their tech, then they’ll buy the game and tear it apart to look to see what’s in it. If they find their tech, they’ll probably contact you asking for proof that you’ve bought it. Or, if they are p*ssed off, they’ll get a lawyer involved. That might mean your game needs to be taken off the market, and you might need to come to some agreement about how much of the revenue you’ve made needs to be shared with the vendor.