I booked the wrong dates and it was my fault. The booking was not refundable upon cancellation and it is also okay. Then I asked the host for shortening my stay. Doing that, I would only lose half the money of the booking. They would keep half the money and then they could rent the place again for the rest of the days. They refused to help me with this, telling that it was the rules that they were given.
If I was a host and a guest made a mistake, I would try to help as much as possible, specially when the request was being made one week before the check-in date.