When I used eBay auctions, I would look at the auctions once a day and address any that I had one or got outbid on.
Please remember that people often have a life and won't be sitting in front of a keyboard waiting for the auction to close so they can pay you. Most of us have jobs that we have to go to that take up at least 8 hours of our lives so we can pay for the things we buy on eBay. And of course, if someone works nights, they may be asleep in the afternoon until it's time to start their graveyard shift.
Be patient. Not everyone is going to respond immediately to messages, and not everyone is going to bid and then refuse to pay you. It's why eBay suggests waiting up to two days to hear from the buyer.
As a seller on eBay, your goal (I assume) should be to sell stuff. You won't sell too much if word gets around that you cancel people's winning bids because they don't respond the moment that the auction closes. No offense, but I know I would never buy from you again if you did that to me. There are many other sellers out there to choose from.
I like to compare this to what would happen in a retail store. If I went to Walmart, they would ask me to pay for my purchase at the cash. But if they then kick me out of the store because I was not ready with my credit card in hand when I got to the cash, I would never be back and warn all my friends not to shop there.
UPDATE: So they clicked on Buy Now. And then their elderly grandmother had a fall and had to be rushed to the hospital. Or he agreed and then was going out with friends and was going to address the issue of payment when they got back later in the evening. There are dozens of reasons why someone might not pay right away. One thing to remember... You should still have the item. Your policy should be that you don't ship until payment is confirmed.
Yes, if they Buy Now and then refuse to pay, you'll have to re-list. But now you can sell for the original price. eBay policy is that if you accept an auction or use the Buy Now, you are committed to that purchase. So complain about the user to eBay and have their account suspended or cancelled.