Supermarkets are businesses, and they want your money. We all have to buy things, but knowing how the supermarkets try to part you from your money can help you to spend less.

Have you ever been to the supermarket to get a few essentials and come away with more than you intended? Chances are you’ve fallen for some of the tricks that supermarkets use to part us from our hard-earned cash.

Appealing to the senses

When you walk into a supermarket, you can smell freshly baked bread, as well as see a display of fresh produce. Our brains have been hardwired to respond to the sight and smell of food ever since people were living in caves and needed to forage for the next meal. Those delicious smells and beautiful-looking fruit are designed to make you feel hungry, because the supermarkets know that hungry people buy more food.

Eye level items

Ever had to ask for help to get a packet down from the top shelf, or had to stoop to pick up a box from down near the floor? A lot of thought has gone into which item goes on which shelf. The most expensive brands are pretty much always at eye level, because supermarkets know that customers in a hurry will get the first item they see, even if there’s a cheaper brand two shelves below.

Packaging

How much does a plastic bag cost? More than you think, if you go by supermarket prices. Do you want to pick some tomatoes out of a box and put them in a bag yourself, or do you want to pick up six of the same tomatoes, ready wrapped in plastic? Be careful: the ones already wrapped cost a staggering three times as much as the same product sold loose.

Special offers

"Buy one get one free” seems to mean the same as "half price”, but watch out! Unless you really need two of the same item, and it’s something that won’t go out of date before you use it, you could be doing the supermarkets a favour. Research found that in England and Wales consumers throw away over 3 million tonnes of food a year, including £2.5 billion worth that has gone out of date. So instead of supermarkets having to throw away unsold produce, you may end up throwing it away for them – and paying for the privilege! And watch out for "Buy three for x amount of money” – it may only be slightly cheaper than the cost of buying three anyway, and you end up with two extra items you don’t need.

Avoid comparisons

Unhappy customers don’t spend so much money, and customers are going to be unhappy if they think they’re being treated unfairly. Because of this, supermarkets will try to stop you noticing their pricing scams. I wondered why the caster sugar in my local supermarket was further down the aisle, instead of next to the granulated sugar. It turns out the caster sugar is 16% more expensive: the same weight of sugar, just slightly smaller crystals, but placed to stop customers noticing the price difference. And remember the plastic wrapped tomatoes? They’re priced by the packet, while the loose tomatoes are priced by weight, so that it’s harder to compare the price.

Impulse buying

If you’ve not been suckered by special offers, the supermarket will try to get you with impulse buying. Basically they want you to buy things that you never intended to buy, just because you happened to see them on the shelves. But they know you won’t buy them if you don’t see them, so they make you walk all round the store. A favourite trick is to keep shifting things around, so that the apple sauce mysteriously vanishes from aisle 20 and reappears on aisle 26, forcing the customer to walk up and down looking at all the shelves. For the same reason, household goods are furthest from the door. Nobody ever buys bathroom cleaner on impulse, but if you want it, you have to walk past everything else to get it. And when you make it to the checkout, feeling like you deserve a treat after all that walking, there are displays of sweets and magazines just waiting for you!