The way it works around here is any guest or visitor that comes to the rental home that does any alterations or damage to the home, the person on the lease is liable for it. That being said, you said he wasn't on the lease...if he's living there, you better get him on it. I've ran into this with "professional housing scammers" This is where: Adult 1 and Adult 2 move in, on the lease, then invite mom and dad and their other 2 kids to come live with them, they don't go on the lease. We let it slide, couple months go by and rent stops coming, we tell them to get out(legal steps, of course), they refuse, we have to evict them, they fight the whole way in order to maximize the time they get free housing. When the eviction finally comes through and they leave, guess who stays...that's right, mom and dad and their other 2 kids. They weren't on the lease, therefore weren't on the eviction order. So, now they have squatter's rights and we legally can't remove them from the property without going to court YET AGAIN, to remove them. Lost 4 months income off that property because of that.