If the customer notices a discrepancy, they give them the lower price. They win out in the long run since it depends on the customer to notice the discrepancy and point it out.
Any minor advantage at their scale wins out as a pretty big deal.
I think a better approach would be to display an initially high price, and mention automatically applied coupons at checkout - or require the user to use their smartphone's app to apply the coupon.
Maybe it depends on the state, and its laws on price marking.
$3.75 each Or buy two and get the second one at 25% off with bonus card.
I suspect that few customers do the mental arithmetic to figure out what their final cost will be.
https://www.recode.net/2018/1/21/16913984/what-does-photos-a...
That kind of fraud is what the corner bodega does, not what Amazon does.
What you described is called fraud.