Intermarché has a 1+1 promo on clips of Cubanisto (Tequila flavored beer). Then the 3 packs of beer themselves had 2+1 printed on the case.
There is no print to say the promos cannot be combined. So of course I expect to pay for 2 bottles and get 4 gratis. Other grocery stores work that way. If there is a promo of that discounts multiple clips and then there are also in-pack promos, you can end up buying fewer bottles than what they give for free.
In the case of Intermarché the register is a bit extra diligent and works out which promo is better then makes adjustments to ensure the promos are not combined.
The receipt shows:
Cubanisto: €3.69
Cubanisto: €3.69
Cubanisto promo: -€2.39
When I saw that I thought something is wrong here… but then I realised the register took the math far enough to offset the in-pack promo. In the end I paid the same price per liter that the weekly ad showed. I think I did not even notice the in-pack 2+1 promo when I grabbed it. So I got the price was expecting and was actually fooled by the receipt.
But anyone could have seen the in-pack promo and expected to get both promos together, and they could have bought the beer on that basis (as I have in the past). And they would have been burnt. There is no regulator for this in Belgium.