This study investigates the successful expansion of BMT Nusantara in Bangkalan Regency which relies on a community-based approach amidst intense financial industry competition. The objective is to analyze the role of Word-of-Mouth (WOM) in marketing strategies and identify the communication processes influencing customer decisions. This research employs a descriptive qualitative method collecting data through in depth interviews, observation and documentation with active customers selected via purposive sampling. The results indicate that customer decisions are dominated by social interaction and validation from religious figures rather than formal promotion. Positive WOM is driven by altruistic motivation and the spirit of Islamic economic advocacy. Conversely instant messaging platforms like WhatsApp serve as effective channels for spreading negative sentiment regarding operational constraints. The study concludes that WOM is not merely a promotional tool but a vital mechanism for social and religious validation essential for the institution's sustainability. Consequently the research recommends implementing Community Influencer Marketing by formally involving religious figures and establishing responsive service recovery management to mitigate digital reputation risks.