Sabbatical house sitting is pretty common in college towns. Often, professors will go on sabbatical from their jobs and also leave the country to go do research. Many are gone for a semester or more and don't want their houses to just sit idle.
I actually got free board for an entire year in college because I house sat for a professor that had gone on sabbatical. We had developed a good relationship over the previous two years and he trusted me enough to let me live in his house for free for almost 10 months. It worked out for both of us.