Fortunately, I don't have first hand experience in this.
But from what I've read and seen on the news:
Yes, your concerns are valid. This has been in the news the last few months. For renting apartments in Paris, it's no longer just "business as usual."
Apparently even the office of the Mayor of Paris has gotten involved. I think they said something like: "we don't want the historic core of Paris to be taken over by tourists, especially if the people they're renting from aren't paying taxes on the rental income."
Also, it was said that the neighbors in these apartments were complaining to the authorities about the constant influx/outflux of transient tenants using the apartments for a short period of time.
We here, wouldn't hear, much about this from posters on this forum, but there is information out there.
We used to have a Paris local who was a regular here, but not anymore.
Maybe Tripadvisors would have some info.
What I've heard is there have been a number of American tourists who had rental contracts and paid their 50% deposit, then they get an email or letter saying: so sorry, the rental is cancelled because the landlord's rental operation was caught in the crackdown.
What I'm doing: We're going to be in Paris for 11 days in a few months and we decided not to rent because of the legal uncertainties, and also in our case, the fact that the two of us only use a Paris lodging for sleeping, it's not like we hang around during the day when we could be out seeing and doing things, and we don't want to do our own cooking in an apartment kitchenette, because part of our reason for our being in Paris is so some professional French chef can prepare that wonderful French cooking for us in restaurants.
Probably it would be ok--but you are absolutely right that there has been a recent and significant change in legal circumstances that could affect you. When it comes to renting apartments in Paris, it's not just "business and usual" or "just like it used to be."
Probably it would work out ok for you, but for myself, I didn't want someone (even an intermedicary) to have 50% of my money and then get a letter out of the blue and then find out how that works, and trying to get a hotel in Paris on short notice, etc.
I am concerned that I may be unduly alarmist over this. You can research this for yourelf on the web. Click Google and then choose News to get the most recent news on the Paris rental crackdown. Perhaps you'll decide to go for it, on the assumption that it will probably be okay (if they didn't have 1/2 your money....).