"Subject to" question

[Joseph Ilg]

If I were to purchase a property subject to existing financing, I am ultimately taking control of the title and the property while making loan payments that are still in the sellers name. Now, if i was a jerk, I could not pay the mortgage and this would further destroy the credit of the seller because their name is still associated with the mortgage payments. Is there any contracts or documents that investors need to provide to the seller which will insure them that I will make the payments and provide a win win for both parties?