Dumb Sub2 question

[Kevin McGarrey]

All,

I listened do podcast number two where the female guest described her first sub2 deal.  She said she offered the seller 65% of market value to which the seller replied "that would be less than I owe on the property.  Long story short, the seller accepted the offer and had to write buyer a $9,000 check.  My question; why did seller have to write buyer a $9k check?