Extra guest fee for an unregistered guest but same number of guests

[Peter2688]

If two guests check in but later swap, for example, 2 girls books a stay and 2 girls check in, but later on you find out that one girl left and spent the night at her boyfriend's but the other girl brought in her boyfriend (unregistered)  who spent the night in your property, should I be able to request and extra guest fee for the boyfriend even though only two people actually spent the night in the room?

[Sarah977]

@Peter2688  I think it might be wise to do away with the "visitors allowed but have to leave by 10". I would make a rule that there are no visitors allowed at all, or only with the host's express permission. Because some people will take a mile if you give them an inch.