Me and two of my friends stayed at Jean's host. The apartment small but very nice and right in the center of Paris. We never met Jean and the keys were given to us by his neighbor and we gave them back to the neighbor when leaving. This was the biggest mistake we did as when we left, Jean filed a reimbursement for 600 Euros for changing his toilet and accused us in breaking it. If you want to live in the apartment, get the keys from the owner, go around the apartment and do hand over. the same handover with the owner should be done when leaving. I would suggest take photos of things as there will be more proof. Now I am planning to do this for all my future trips.