We own a holiday cottage in a fairly remote area. There are two bedrooms, both with double beds, but after the place was wrecked in the early days by a bunch of four young men, we made the decision to limit the numbers to two guests only. A couple of years ago we took a booking, and as usual my husband was there to greet the guests upon arrival. They got out of the car, and my husband showed them around the property, but as he went to walk away, he noticed movement in the car. Thinking it was a dog, which we don't allow, he queried it with the guests. It turned out that they had brought 2 teenagers with them, and had clearly told them to keep their heads down when they saw my husband, not realising that we actually live next door! They told us that as there are 2 double beds in the property that the boy and girl would just bunk in together. They were told in no uncertain terms, that while the cottage has 2 double beds, we only rent to TWO people, therefore they were in breach of contract, and couldn't stay. They came up with all sorts of excuses, but as we were using an agent at the time, we passed the phone to them to deal with it. They were told that they must vacate with immediate effect, and as they'd arrived late, (we're sure in the hope that there would be no one to see them), they not only lost the holiday that they had bought and paid for, but also had to pay for a hotel for the night for the four of them! I did feel a bit guilty, but as 4 people in the property would have voided our insurance, we weren't prepared to risk it, and let's face it, people who try to pull this sort of stunt are hardly likely to be the type to take care of the place, so we felt justified in sticking strictly to our Terms & Conditions. So OP, you might like to make sure your friend is aware that this could be what happens to them, if they decide to go ahead with this devious plan.