i work in a high street branch of a major retailer
not much of the stuff is priced on the packaging, most of it has a ticket on the shelf
as part of the due diligence for the store, the price tickets have to be checked for accuracy and replaced if incorrect - if something is ticketed at a lower price than it should be, then the item is sold at that lower price(someone would then remove the wrong ticket and replace it with the right one)
if the ticket price is higher, then the customer gets the item for the cheaper price anyway (maybe the tills would have to be checked)
AFAICR this falls under the remit of 'trading standards' and if we got a random visit from the trading standards officer, who then found that a lot of tickets were wrong, legal action could be taken against the store
i too have heard the thing about a priced item being merely an 'offer' to sell the item and all that, but i suspect if a store was found to be habitually wrongly/under-pricing items (whether deliberately or through couldn't-give-a-tossness), trading standards would (or certainly should) be all over them
these days, they would be likely to go through all paperwork to ensure there is an acceptable system of 'control' in place, much like there is with expiry dates on food, weights&measures issues etc.
never mind writing to the CEO, go where the power is - 'raw deal' in the sunday post or 'the judge' in the sunday mail!