Shoppers are using a 'get out of jail free card' to steal from self-service checkouts, costing Coles and Woolworths an estimated $1 billion a year.

Canstar Blue recently surveyed more than 2,200 shoppers, with seven per cent admitting to deliberately not scanning items.

Another nine per cent said they had scanned a product at a lower price when using a self-service checkout.

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Sixteen per cent of surveyed Australians have admitted to either deliberately not scanning items at self-service checkouts or scanning products at a lower price (stock image)

Fresh fruit and vegetables are the most common items stolen by shoppers using self-service checkouts (stock image)

Fresh fruit and vegetables were the most common items stolen (24 per cent), followed by packaged foods at 16 per cent and snacks and drinks (12 per cent).

'In most cases, those people caught out trying to steal simply try to blame the machine, or claim it was a mistake,' Canstar Blue Editor Simon Downes said.

'These excuses seem to be seen as a 'get out of jail free card' because mistakes can genuinely happen.

'The challenge facing the supermarket staff on the front line is working out who the real offenders are and who simply made a mistake. This is where the eyes in the sky and any other tactics the supermarkets have to catch offenders come into play.'

Packaged foods were the second most common item shoppers took without scanning the product at a self-service checkout (stock image)

NSW and Victorian shoppers are the main culprits when it comes to thieving at self-service checkouts, while those in South Australia are the least likely to steal.

Of those who admitted to theft, only five per cent said they were caught in the act.

'It's also worth keeping in mind that this survey reveals the number of people who to stealing. The true figure may be higher,' Mr Downes said.

A Coles spokeswoman told news.com.au they have trained covert security officers in their stores across the nation and 'they're catching hundreds of thieves every week and reporting them to police'.

Woolworths said while the majority of customers do the right thing at self-service checkouts, they had security measures in place for those who don't.