I work days at a Walgreens in NW Arkansas. If the tags says one thing, and the item is another, we give it to the customer for the tag price, UPC notwithstanding. Now, if it says "Keebler Cookies, 14oz", and they have a 64oz box, they're not going to get it. We expect people to READ the tags, but its stupid to expect people to check the UPC.
Also, we have weekly sales that end Saturday night. Sunday morning, we are bound to have customers find ad tags from the previous week on the shelves. We ALWAYS honor them. If the volume is low enough, we go back and grab the tag off the shelf. If not, we page someone who isn't as busy to go get it.
Try shopping at a more customer-friendly store. I never thought I'd enjoy working retail, but where I'm working now, there is honestly a good deal of care for our customers, and the workplace is better for it. There is also respect between employees, and get this - TRUST. If I'm working the register, I don't have to call a manager for every little thing. I can change prices, do exchanges, give and accept rainchecks - on my own. The only thing I need a manager to do when I'm doign register is a return, that requires the little manager's key. I'm told the only reason this is done is so the paperwork is more centralized, and every employee doesn't have to handle return paperwork every day.