Where I live, we don’t yet have those cards. I despise the idea of them and hate getting caught out by them (I’m looking at you Tesco and Lidl).
Normal price for something - 0.49 (in stores without these cards) But in their store it’s only that price with their ‘club card’ or ‘plus membership’.
Otherwise it’s 1.59
There are loads of other items with high markups.
BUT - the marked price is the normal store price to the inexperienced shopper of these data collecting stores, with the blind spot being the need to have a store card to get the ‘discount’. My full shop was an extra 103.46 altogether between the two stores (51.22 in one 52.24 in the other) rushing to get christmas dinner and dining and extras. Should be banned. /rant
The government doing a sick job of protecting consumers. /s


Historically, the whole point to the loyalty card coupons was because then they could track your purchases and sell that data on you.
It used to be incredibly valuable, and it techncially still is. But your big box retail stores are going to insane lengths, including tracking you from the moment you pull into their parking lot (including knowing what kind of car you drive,) and how many times you circle, lets say, the lego aisle, or the cookies. They know how long you spend looking at stuff and are selling all of that. (as well as using for marketing to sell you more shit you don’t need.)