I was watching the bidding on a lot of three five packs. The bid was at 17 when someone decided to "buy it now" (and pay more than he had to), and threw up a bid of 25. The lot closed at 25, 21, and 19, with the bid of 19 going up AFTER the bid of 25.
There is no need to add the "Buy it Now" because it is already built into the auction. You can throw up a bid that is just under retail, but higher than a lot has ever sold for because that is where the "buy it now" price would be set. But only if you are determined to pay more than necessary, in order to save a little work and eliminate the fun of the auction process.