Local law governs this type of situation. In NYC it is illegal to charge more than the posted price. I have heard that in colorado the price in the computer (scanned price) is THE price the store must honor and if there is a discrepency between the posted price and scanned price, the scanned price “wins”.
Sounds to me like someone in the store is lazy. The salesperson was likely not he owner and I wouldnt blame him/her for not honoring a lower price if he/she would be responsible for the shortfall.
Are the signs still hanging 3 days after your incident in the store? If they are, sounds to me like a serious case of bait and switch.