If you just mention it to the cashier they should just radio to either AP or customer service who should look it up on the computer and give the thumbs up. Save the ink.
That's how I make my store roll. Cashier radios me, I check the site and give the thumbs up or down.
*forgot to add that when the cashier goes to the price match screen on the register, one of the competitor options is bestbuy.com. Best Buy matches the website no questions.
American Psycho on blu ray for $9.99 = win.