Does anyone have any experience with renting an apartment in Paris from Welcome2France?
No experience with that company. Rick's books list 9 other apartment rental resources for Paris, including AirBnB, if you need them.
There are reports that Paris authorities are cracking down on AirBNB rentals in particular so you do run the risk of no place. Most all Paris rentals are illegal and Air BNB often adds to that the fact that they are sometimes illegal sublets.
I've used VRBO in Europe and the U.S. quite a few times, including several times in Paris. Homeaway is their sister company. Many here also recommend Vacation In Paris. I've never heard of Welcome2France.