DealMachine can tell you mortgage information for a property whenever applicable.
That's useful because it allows you to see the equity they probably have in a property. If they owe more than you can offer, they wouldn't be able to accept your offer even if they wanted to!
To see the mortgage info, simply add a deal in DealMachine.
Scroll down until you see "Mortgage Amount". This is normally listed together with the Sale date, Sale price, etc.
Note: if you don't see any Mortgage Information for this deal, we were not able to gather any info for this particular deal. Try adding another deal!