@Leanne177 It sounds like you've already checked the guest in and allowed him to stay. In which case, it's a bit too late to take any other action.
You would've had reasonable grounds to refuse admission to the property, but in doing so you would have forfeited your payout. Neither of your options was a good one.
My thought on this would be, if you're going to allow last minute requests , you should get the important questions out of the way before hitting accept. (surely if you care who turns up you can't possibly be using Instant Book?)