It amazes me that there is an article playing this up as a “trap” that needs to have an “alarm.” Its a trap for stupid people. If you need a couple of the items, then “spave” to get the extra. If you only need one, then only buy one. If you are so stupid that you buy two or three even to get an extra even though you only need one, you need adult supervision when you shop.
Too many people don’t realize that on some grocery items, “buy one get one free” deals mean if you just buy one, you get it for 50% off. Check the label to see if you actually have to buy two to get the discount.