Word of mouth is expected to be objective, unbiased and complete because it does not come from the company. So, if you are using well-known industry experts to advocate your product, they better be telling all sides, including a fair assessment of the disadvantages of your product, or their credibility will be destroyed. They will look like salespeople, who, like advertising, are expected to present the product in the most favorable light. Word of mouth is looked to as the only place where people can learn the downside of the product. If it is not there, credibility is totally destroyed.
Word of mouth is, in fact, the only fully honest marketing technique.