It could well be a repossession or maybe it's being sold following a death, and the family can't get there to clear it out.
I refuse to believe that anyone would have estate agent photos taken with their house in such a mess, if they were actually living there.
Though I have just remembered a house dh and I viewed, that was being lived in by the estate agent (I think they were friends with the vendor, hence being allowed to,use the house), and it was a complete tip - there was even a used nappy on the floor upstairs!