There's no shortage of stories where customers go crazy for free giveaways at the supermarket - and one expert has revealed why this is the case.

Between coffee shops offering a free drink after you've bought 10 or beauty retailers handing out samples if you spend enough, research has explained this is all another marketing trick to hook people in.

University of Canterbury marketing professor Ekant Veer says people like to feel like they've won things, especially if they're free.

"We feel like we're getting rewarded for our loyalty or rewarded for our good behaviour, and then it's going to work for us. We're going to get that little dopamine hit." 

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