Evangelism marketing is an advanced form of word-of-mouth marketing in which companies develop customers who believe so strongly in a particular product or service that they freely try to convince others to buy and use it. The customers become voluntary advocates, actively spreading the word on behalf of the company. As they act independently, evangelist customers often become key influencers. The fact that evangelists are not paid or associated with any company make their beliefs perceived by others as credible and trustworthy.