I looked at a room for rent in Philadelphia. The house is owned by a person who said they travel most of the year and are at the house only a few weeks each year. They want a security deposit about a month before moving in. How can I find out if the person is legit or if they are going to take my money and run? He wants a month to month deal, but I don’t think the guy has a rental agreement for me. He said that once he gets the deposit he will give me a key to the house. If I printed up a sample rental agreement found online and made him sign it will it hold up as a legal document?

It should be legal, it sounds pretty normal. However, do not give cash and use the meo section of your check put the address of the property and that this is a security deposit.
I have also provided a website for links to read up on the laws for your state. Hope it helps!