When I see a range listing like that, I’m still pretty sure they want the $649K and have the low range there just to attract offers (ahh the idiotic brilliance of range pricing).
Since it’s possible that they put down $30-120K in the first place (probably the lower of the two), they might have some room to avoid bringing cash to closing. Even so, a tough loss to swallow.
If they really had to come up with $100K, that would sound tough, but I guess it depends on their circumstances. They might or might not have that kind of cash (or equity) somewhere. This listing seems to have signs of RE “investor” idiocy, but there could be more to it.