We won't be undersold
If you have a won't be undersold motto, the very best thing that you can do is find customers who find a better price somewhere else... and then give them the discount. Why? Because it proves you're not lying, and it spreads the word. Those customers are heroes.
Compare that approach to this one from Jason found at courant.com. It appears as though Best Buy had a secret Intranet site that looked just like their regular site... except with higher prices on it. So, if you came in claiming that the store was being undersold by the website, it's alleged that employees would show you a site that sure looked like their site...exept you were 'wrong.'