Just touring somewhere isn't going to help, you have to make sure the person who is showing you the apartment owns the apartment, look up real estate records and ask their the landlord's ID. I say this because there is plenty of cases where scammers will break into vacant buildings and "rent" them as long as possible. Heard of a story where a guy was living overseas for a few months and came home to a family living in his house which had been "rented out" by a scammer who broke in and changed the locks.
I believe in some states its not even a matter of saying "Hey this is my house get out" you have to go though eviction processes to remove them as well. What a mess.
Yes, absolutely. Tenantancy is usually established after around 30 days of continued occupancy and once they are tenants, even if they aren't paying rent, you can't legally kick them out without going through the proper legal channels.
There's even been cases of people posing as fake real estate agents to "rent" apartments. If your dealing with a real estate agent then ask for their ID like you would a landlord, and the license number, and look up their real estate license online.