Can I get Seller Financing when seller has a mortgage

[Zackary C Dunn]

Hey everyone, I’m a newb so don’t roast me to bad for a stupid question. I have an off market opportunity that I had the seller on the hook at 57,000 if he finances for 18 months with a balloon payment and zero interest. Come to find out he has a mortgage balance of 57,000. I offered to do a lease with option to purchase but he was against it because as he says there is nothing locking me into purchase other than my deposit. Any ideas would be much appreciated.