I consider the item mine until there is a winning bid, then it is yours. I will end an auction with no bids at my discretion. I sell what I would buy. Most of my auctions are thing I have owned for some time and am giving them a new home.
I am gonna say this here, I buy a lot on here too. I always pay right after I end someones auction because basically the seller is now storing an item for me. I think some kind of contact if you can't pay right away is simply being respectful of the other person and their time and energy. Communication is golden!