Laws surrounding Subject to/loan assumption

[Daniel Lambert]

I was doing some research but wasn't coming back with anything form a legal stand point. But are their laws that restrict when one is allowed to do a subject to deal? Ie. does the seller need to be in, or close to, pre-foreclosure, or in a tough spot? Or can you do a subject to deal under any circumstances? 

I have a cousin in Florida that is moving and would love to come to an agreed price on their place but just take over the mortgage instead of securing my own loan as I am looking for it as an investment and would be required to do 20% down (which I would not have).