Purwati, Astri Ayu, Tomy Fitrio, Frank Ben, and Muhammad Luthfi Hamzah. “Product Quality and After-Sales Service in Improving Customer Satisfaction and Loyalty”. Jurnal Economia 16, no. 2 (October 30, 2020): 223–235. Accessed June 6, 2025. https://journal.uny.ac.id/index.php/economia/article/view/31521.