There are many online vacation rental agencies that list millions of short-term rentals worldwide, allowing for more competitive and cheaper rentals. In some cases, the rentals are rooms in a house; sometimes it's the entire house, sometimes fabulous mansions. In most cases private owners are the ones listing their places in the online sites.
We used Home Away to find a wonderful apartment in the Saint Germain District of Paris, right across River Seine.
It was a flawless transaction although I should mention that I was diligent in checking the reviews of the apartment. One is advised to check the reviews carefully and to make sure there are many reviews, not just a few, because there are scammers who list in these agencies. I also called and talked to the owner/manager directly, and was careful to pay my deposit with a credit card. I had copies of all email-correspondence as well.