Shopify Buyback System for Customer Device Sales with DHL Integration

I need a Shopify-integrated system that allows customers to sell their devices to me through my website. Customers should be able to select their device model, answer specific condition questions, and get an instant price estimate. After accepting the offer, the system should generate a DHL shipping label for the customer. Once I receive and check the device, I want to manually review its condition and send a custom offer if the grade differs, with automated email notifications to the customer about any updates or new offers. The system should use manual payment processing and integrate seamlessly into my existing Shopify store. Ideal skills: Shopify app development, experience with DHL API, email notification setup, and user-friendly UI design.