Mitre 10 drew the regulator's wrath after advertising a "20% off storewide sale" in February this year but didn't disclose Cash-savvy consumers are probably already aware that such sales are rarely absolute (you'll never see consoles including in "10% off all toys" sales, for instance), but the failure to disclose those terms in television ads and online was what got Mitre 10 into trouble (it's made legal undertakings to ensure it doesn't happen again).
The business lesson? Make sure you disclose adequately. The consumer lesson? Check carefully before buying sale goods.
Picture from Wikimedia Commons