She booked for only one person being aware from the beginning that they were 2 and even if I told her to book for 2. So when they showed up at the apartment I gave them two beds asking them before leaving to pay for the extra bed. The problem was at the end because they didn't want to pay pretending that the extra guest didn't enjoy the stay and this exempted her from paying. An objective conclusion is that they planned from the beginning to try to rip me off, not following the rules. If they didn't have enough money they should have told me and I would have given them a discount. Unbelievable.