You should always check that the entertainer you hire has sufficient insurance cover in case of an accident.
I have Public Liability Insurance Cover for £5 million which can be shown on request.
In my over 40 years of calling I have not had a claim as I am always conscious of health and safety issues.
Another “legality” is the PPL music licence I hold which permits me to use commercial recordings at public functions, for which I have to pay an annual fee. Not all callers are so licensed but the authorities can stop an unlicensed function and confiscate the equipment.