While going to a supermarket today my parents specifically asked for some bags of peanuts that were on sale as usually a 900g bag was about $6 and now it was on sale for about $3. When I arrived at the supermarket all the prices were still tagged as a non-sale price. I doubled checked again online on my phone and sure enough it was listed at $3. This store just happened to not have price scanners for the customers as well.
At minimum I knew the store would price match so I just took two bags to the self-checkout. Sure enough, it actually rang up at the sale price which meant the staff just simply didn’t bother to change the price tag on the shelf. There is no other real way of knowing this item was on sale too unless you checked ahead of time. A good example on how you should try and check prices ahead of time nowadays before going to the store.
It’ usually only the store specific clearance items I tend to expect to find some random surprises. But for items I am specifically thinking of buying I do tend to check ahead of time.