I sometimes go to a local supermarket to buy lunch. I usually fill a medium salad bowl at the salad bar which costs £2.99 alone, and pick a drink worth £1.75. Total £4.74. However, both these items qualify for the meal deal that is £4.00 total, but to get that meal deal I have to take a “snack” too, although I rarely want any of the snacks on offer. If I walked out with just the salad and the drink and paid only £4.00, I’d risk being accused of shoplifting having not paid the correct price for the goods I had taken. If I pick up a snack, bringing the notional total to well over £5 (sometimes even £6), I can legitimately pay only £4.00 even though I don’t want the snack and could even throw it in the bin as soon as I leave the shop. Most people appreciate [and accept, maybe grudgingly] that a supermarket meal deal involves picking three items, one from each category, in order to get the deal - and if they don’t go for all three they have to pay for the individual items even if just two exceed the price of the deal. In other words they play by the supermarket’s rules and maybe sometimes acquire something they don’t really want or need.
What baffles me is that many people accept that a supermarket has a right to set pricing rules, but they would probably be the first to complain about the railway’s rules for advance tickets, which clearly state that the entire journey must be taken without stopping/starting short, on the correct train, with no breaks. Moral of story: if you want the deal, stick to the rules.