You are wise to be careful. The actual owners may be named Johnson, but the scammers can just set up a fake email with that name. Do not send money away for a deposit and hope the keys come back in the mail. Do not fall for a way below market rental for someone who "just wants someone to take care of the house."
There are variations of rental scams all over the place so make sure you are dealing with the actual owners and or licensed representatives.
Good luck to you. As you did not give us a link of the address so we could look it up for you.