One of the oldest marketing strategies and still the best is Word of Mouth. Just need to be upgraded to the 21st century, hence Word of Mouth Marketing.
A Nielsen study found that 83% of people trust recommendations from people they know.
Word of mouth Marketing is different from “normal” word of mouth as WOMM is intended to create Proactive word of mouth. By creating such a remarkable experience that the customers proactively spread the experience they had (they want to tell a friend), instead of being prompt to do so (like a friend asking for a good plumber).