I think as long as the store is consistant there shouldn't be a problem and in the pic I posted there is no question of deception. On the 2 occasions when there has been a difference between marked price and till price they have always honoured marked price, apologised and created a new sign to correct what is presumably a head office error.My local B&M, I have stopped going to. There will, for example, be a 3L bottle of coke on the shelf, the end cap price will display the price of a 2L bottle.
I resorted to using my phone to find the correct price. I did email head office about the misleading prices. They didn't give a toss. You mention it to the staff, they don't give a toss either. Sorry, I have not intentionally hijacked your post, but in my opinion, the retailer should be upfront and honest. If you have end cap prices above (or below) a product, use arrows to let the customer know what thy are looking at.
Not hijacked my post, this has come a long way from advising tools for a newbie.