Deed to contract question

[Lincoln Slonaker]

I have a question regarding deed to contract agreements. I am a first time investor and still learning especially when it comes to owner financing. If the current owner has a mortgage out on the property how can I get this place locked in still? I talked to a real estate attorney and he said that there is usually a clause preventing any secondary loans being held on the property. Hopefully I just misunderstood him because I was not aware of that. Thank you for any information!