Do you agree that "by word-of-mouth" is the best means of advertising?

Does empirical research support this premise?

'By word of mouth' being 'speak as you find', this would be a more encouraging way for a consumer to try a product, if others have tried it and found it to be successful. Whilst advertising may make a consumer aware of a product and give them the opportunity to find it and buy it; all the advertising in the world may not completely convince consumers that the product is for them. To actually hear from another consumer how the product has performed for them, has to be the wisest endorsement.