This research aims to study customer service behavior, satisfaction levels, and demographic characteristics influencing satisfaction, the relationship between service behavior and satisfaction, and the relationship between satisfaction with services and Net Promoter Score (NPS). Data were collected through online questionnaires from 348 regular customers. Statistical analyses included independent t-test, one-way ANOVA, and chi-square tests. The findings reveal that the majority of customers choose the Government Savings Bank due to its convenient location near their residences. Most customers visit the bank 4–5 times per month, primarily for deposit, withdrawal, and money transfer transactions between 8:30 AM and 12:00 PM. Overall customer satisfaction is high, particularly in the area of marketing promotions, which received the highest satisfaction scores. Demographic factors such as gender and average income significantly affect satisfaction, while service frequency is correlated with satisfaction. Moreover, satisfaction with pricing, marketing promotions, and service personnel significantly correlates with NPS, which was recorded at 83.33%, indicating customers’ strong willingness to recommend the bank’s services. The study suggests that the Ban Na San branch of the Government Savings Bank focus on tailoring products to meet the needs of female customers and middle-to-high income groups. Enhancing efficient and convenient service delivery to accommodate frequent customer visits is recommended. Providing transparent information on service fees, promoting marketing through loan product brochures, and increasing staffing during peak hours are critical to ensuring high-quality service. These measures are expected to foster customer loyalty and encourage positive word-of-mouth recommendations.