Tell the Seller you plan to have an attorney review your terms before you agree to anything. That way if the Seller is a scammer he may not call you back!
You have to be very careful because there are some sellers that are in pre foreclosure collecting rent to own, owner financing money and then the house ultimately gets foreclosed or a short sale is done. You don't want to pay more than the fair market rent if the owner owes more than the house is worth and ends up getting foreclosed on.
It may be legitimate, just try to have an attorney review before you sign.
All the best,
PS Larry Fuentes with Fuentes and Kreisher is one of the most experienced Real Estate attorneys in Tampa Bay and his fees are also very reasonable http://www.fklaw.net/