How can I find out whether a business has "hidden" liability insurance? -

You ask them. Liability insurance is NOT required by law, anywhere. The existance of liability insurance for a particular entity is private information. Sometimes it's required by contract, but again, you'd have to be party to the contract. You can bring suit against said business, and see who defends against the suit, and who pays if you win. what and why? You can't other than by asking them. There is no way to find out this information. There is no central database of who has what policy; the other party's insurers are not obliged or allowed to give you any information about someone else's policy (or even that a policy exists) nor is the business obliged to inform you of this information either. You will have to sue the business, at which time the business will file a claim with their insurer or not.