It's not often that a major supermarket admits out loud how it tricks us into buying stuff we don't want, so we should be grateful to Tesco for last week's startling admission: much of the bagged salad bought by customers ends up in the bin, especially when it's bought in a two-for-one offer.
Tesco discovered that 68 per cent of produce grown to be used as "salad leaves" is thrown away; 35 per cent of it once it gets to our homes. Other products that end up in the bin include grapes, bakery products and a fifth of all bananas.
At the same time, it was "revealed" that supermarkets' price-match offers tend to be a bit of a swizz. A report by Which? found that each store tends to "skew" its comparisons, which accounts for the hitherto unexplained fact that every supermarket claims to be cheaper than every other.
While the supermarkets are being so honest, I'd like to know the answers to some other grocery-related puzzles. Such as, what do they do to avocados to make them rock hard until the moment they turn brown and mouldy? Even the ones that are more expensive because they are supposedly sold "ripe"? It is a weird fact in Britain that you can only buy a decent avocado from a small high-street greengrocer, preferably run by immigrants, and that supermarket vegetables are little more than coloured water made into funny shapes and frozen there until the second they get into your fridge.
"I think we have a moral obligation to help customers realise the benefit of buying ugly fruit and veg", says Matt Simister, Tesco's group food commercial director. Let's not quibble about what it looks like – can we just have it edible, please?
Another strange way that supermarkets help us "save" is by giving special offers to loyalty-card users. If you tend to go shopping once a fortnight and spend exactly £50 on your regular purchases, the voucher you receive at the checkout will expire in 12 days and only be redeemable when you spend £60 or more.
You'll also be given a fistful of vouchers for something that you've just bought a year's supply of, and you can't give them away to the person behind you in the queue because they are tied to your own loyalty card.
You too can play the middle-class game of trying to trick the system by doing your shopping in ever-decreasing relays, but it's like trying to beat the banker in a casino.
Not only does this encourage waste; it discourages the at-checkout philanthropy that is one of the few ways we can all get one over on modern life.
Ending two-for-one deals on items that perish within seconds of getting them out of the shop is a positive step by Tesco. But a better idea would be the post-checkout food share. Buy two bags of satsumas for the price of one, and then leave one of them in a box for the next customer. Less waste, cheaper food bills and more friendliness all round. Come on, Tesco: every little helps.