I just went through this. We just booked an apartment in Paris for a month and a half beginning the first of October. We stayed in the same apartment (upper 9th) the last two years and was hoping to stay there again. I wrote to the owner over two months ago saying we’d like, once again, to rent her apartment. Long story short: she has rented it to somebody else for a longer period; she let us know about that the beginning of April.
We’ve used Airbnb the last five years for Paris rentals, so that is where I turned to first. A couple things about that. The city of Paris had sued Airbnb (for $14 million) to stop so many unlicensed rentals. I won’t go into the details, but it now seems that an owner can use Airbnb without fear if the owner (1) registers the apartment with the city, and (2) caps the number of days per year the apartment is rented out to 120 days.
Here’s a writeup on the Registration Code:
https://www.airbnb.com/help/article/1634/what-is-the-license-or-registration-number-field
So, if you are going to use Airbnb, I would make sure the rental listing has “License or Registration Code” followed by the registration number. It will be displayed at the end of the owner’s description of the apartment. If the listing does not have the registration number, I wouldn’t take a chance on the place. I said “without fear” above because of a recent situation in Miami. People from some Miami department went through a very popular neighborhood for Airbnb rentals; went to each apartment and if the apartment had renters and was not registered, the renters had to leave. That day.
The only agency in Paris I’m familiar with is Lodgis. They seem to have a good inventory of apartments. HOWEVER: watch out for those fees and charges! They are not all explicitly stated. One apartment I looked at was more-than-reasonable at €1515 per month, but the Charges were €170, the agency fee €900, and the security deposit €843. So, if you’re going to work with an agency, make sure about the total cost.
Another word of advice: don’t pen yourself in on location. Nothing else in the 9th appealed to me at our price point, so I looked in the other north arrondissements: the 17th, the 18th, the 19th, and the 11th. I even looked a couple times (heavens!) in the Left Bank. The apartment we just rented is in the northern part of the 10th.