When closing a supplier, it's essential to focus on the mutual benefits of the partnership. Highlight how working together can drive sales, increase brand exposure, or streamline operations. Express interest in a long-term relationship and be prepared to address any concerns they may have, such as drop-shipping or authorized retailer issues. Emphasize your commitment to meeting their requirements and ask for feedback on how you can better align with their needs. A phone call allows for a more personal touch and immediate feedback, which can help build rapport and address any concerns more effectively.