we could easily show that the promotion is no longer valid by pulling up our website that day to prove that the ad is no longer "published" there.
Yeah, I thought about that, too. Here's why that would fail:
1. Sweet CD rate promoted across all channels, including your website.
2. Interested person prints ad copy in a way that doesn't show the date printed and squirrels it away.
3. Six months later, rates have dropped significantly and you've long since ended this promo.
4. Customer tries to pull a fast one and is politely told by CSR to pound sand.
5. Customer waits a week or two and then sends a formal complaint to your regulator. (Sending it to the wrong agency will drag it out and delay your regulator's investigation another week or two.)
6. Regulator contacts you as part of it's investigation of the consumer complaint...by this time, the promo's been dead for many months and it's been at least a month since you refused to pay the obsolete (higher) rate. How will you convince the regulator what was or was not on your site a month ago?