Yes I can undestand if you received a bog-standards entry you may not want to pay.
A simple way to counter this is in your opening post to simply state that you reserve the right to withhold a winner from the contest and withdraw the thing compeltely if lack of participants. At the end of the day a few senteences like this and there would be no arguments. Seen.to would not feel aggrieved at the contest being ended as he would see that the terms say someone may not win, but as it was someone had to win, with no back covering, leaving the whole mess in the first place.