If you see somebody crawling along the floor next time you're in the supermarket, don't be alarmed: they may just be checking for bargains.
Most of us simply trot along the aisles grabbing a tin of beans here and a bottle of ketchup there, as they catch our eye.
But according to MoneySavingExpert, you can get much better value for your money by checking out the lower shelves. Here, it says, you'll often find the same branded products in different sizes - and offering much better value.
"Some of the branded products that caught our eye included Yorkshire Tea teabags, which were 58% better value on the bottom shelf compared with the same product at eye-level, as well as Pot Noodle, which were 52% better value and Hellmann's light mayonnaise, which was 47% better value on the bottom shelf," says the firm.
Of course, you may need to do a little maths to work out what's best value - although stores these days tend to list the price per 100g or 100ml on the shelf label.
And you'll often find that even when there's a special offer on one size of product, another, less visible, size will be better value.
"You can see this clearly with the Lurpak butter example [at Asda], where if you grabbed the two for £5.50 offer at eye-level, you'd be paying 50p more for the exact same weight of the same product on the bottom shelf," says MoneySavingExpert.
It's also on the bottom shelves that you're likely to find supermarkets' own-brand ranges - which can be way cheaper than branded alternatives.
At Asda, for example, Twinings teabags are 87% more expensive per teabag than the company's own-brand product in the bottom left-side corner of the display.
Similarly, at Sainsbury's, Dove soap is 84% more expensive per 100g at eye-level than the own-brand soap in the bottom corner.
It's not the only way stores arrange their layout in order to get you to spend more. They place staple items as far apart as possible, for example, hoping you'll grab a few other bits and bobs as you make your way from one to another.
And while there's a growing trend to remove sweets and treats from the checkout, supermarkets have other ways to tempt people into impulse buys: in the 1990s, one US supermarket is said to have placed beer next to nappies on a Friday evening, targeting men asked to pick up nappies on their way home.