Used Mobile Sale Purchase Android App

I need an Android app for used mobile purchasing and selling new mobiles online. Source code will be our property. Project will be awarded after you show us your work flow document only. Milestone will be created and released after you show us 50% of total work. I want that people download our app and scan their mobiles online and app should tell them estimated cost and ask them to agree for selling their mobile and if people agree to sell their mobile then, app should take customer's address and that query should be sent to our technical team. After sale query is raised, a ticket number will be generated and will go to technical team, admin and customer. Their will be two Apps One for technical team and another for Customers. Technical experts should be able to sign up on the app and their app will be connected to customer app and admin panel. Database should be on Google firebase. Sign up should be done using mobile number otp authentication in customer and technical team app both. Once any mobile is posted for sale, technical team will visit the customer's address and collect the mobile. Once technical team start visiting any customer, a notification will go to customer that technical champ is coming to your address using Google map. Customer should be shown to technical team and admin on Google map after she/he finish his/her mobile scan and agree. After mobile is collected, customer, technical team and admin will get a notification in their panel that case is closed and payment is made. If customer has any problem with anything, they can create a support ticket and ticket number will be generated and will be stored in customer and admin panels. If complaint is about technical team then complaint i.d will go to technical department also. Customer can chat with Admin and Technical team also. After people raising the query to sell their mobile on our app, a page of new mobiles available with us should open on their app. Where people select any mobile of their choice and add to cart and purchase. Any images of the mobiles should have a validation of 1000*1000 dimensions only. Users should directly open our app, signup and start surfing. If they want to sell their mobile or purchase any mobile, then app should ask their complete address, email i.d etc. They can download their invoice anytime from their panel. In technical team app, their should be all the details available Everytime that this expert was given these many calls and he closed these many calls. Admin will be a marketplace who will provide leads to different Technical experts. Not purchase mobiles directly.