i would need to go and look it up, it's been a while since i studied A-Level Law, it's related to contract law and the disclosure of payments.
as to your second point, not only are these not 'hired actors' they are 'paid social media personalities' and i use that with so much looseness it might as well not be attached at all, as stated the only reason they are there is because 1) they fit within the tickbox framework set up by Amazon for how many of a certain minority they need to have present, and 2) they are small enough 'content creators' to be considered 'unknowns' but large enough to have an audience that Amazon felt was worth interacting with.
also as stated, they didn't disclose that they were paid (through hospitality and other things as detailed previously) which for the service they provided is illegal here in the UK, it was only due to the 'negligence' of one of the attendees of the event that people found out the extent of what was given in order to get these clowns to provide a positive review of hwhat they were shown.