Word of Mouth is the act of consumer providing information to other consumers.
Word of Mouth Marketing means giving people a reason to talk about your product or brand and forward it to others. WOM acknowledges the importance of customers endorsing their products or brands. WOM is the most honest form of marketing. By its very nature, viral marketing campaign is unlike which has been done before which means there is no formula,no stats and no guarantee in advance. Results can only be proven retrospectively by which it can be too late for those results to have any more meaning than the knowledge that viral marketing works in priciple. Even the successful campaigns of past wont be able to replicate same kind of success if used by competitors. It’s very high risk and high gain means of marketing. Also the cost is not measured in financial terms but in the way customers perceive the brand. For this to happen, viral campaign must be able to stimulate emotional resposne from the prospects.
The campaign should not be fake otherwise same campaign can backfire. I am not sure if there is any empirical evidence which proves if it really makes difference to the bottomline. Much like television advertising, it is not always clear wheather people have purchased a product due to TV commercial or due to varios brand promotions across various platforms. All I can say is it works.