When someone interacts with a business, they can tell others about their experience as a way of validating a business or steering people away from it. This is something that the digital age has made increasingly possible, as anyone can now leave a review about a business somewhere.
They might submit it to your website, post it on social media or enter it into one of the many trade specific review websites. As this is such a common thing to do, it is now one of the first things that new customers turn to when they consider working with a business or buying from them for the first time.