Huh?
You see an item for $3.50 so you take it off the shelf.
When you get to the POS, the price has been changed to $4.00, but you caught it and mentioned to the cashier that it was $3.50 when you pulled it off the shelf.
So, the cashier sends a stock boy to do a price check and confirms it is $4.00, because the price tag is electronic and can be changed remotely.