Refurbished Gadgets Price Comparing and Sales App

I need an Android app. I would like it designed and built. Payment will be made according to Milestones creation. Each payment will be released after that percentage of work is finished. Nothing will be paid in advance. First payment will be released after completion of first milestone which includes the price comparing feature from other apps. There will be customer panel, partner panel, admin web panel. All the signup will be done by OTP authentication. One mobile number and email i.d can be used only once to signup. We want you to develop an Android App which could offer price comparing feature of old and refurbished mobiles. First you need to understand the formula of selling refurbished mobiles on mobile app. User first upload the mobile picture, list of available accessories, condition of mobile etc. After that app gives the price of the mobile phone, if user accepts it then it sends confirmation greetings message and email to buyer. Same formula is used by all mobile apps. We want that you integrate other refurbished mobile selling platforms in our single platform so that when user enter all the required details on our app, it should search with other apps also to get the best price on screen for customer. So that customer could sell their mobile to the platform which is offering maximum price for their mobile. Similarly if any user want to purchase any refurbished mobile then also user search that mobile model on our app, it should search all other apps on integrated with our app and show the best price with different results of that mobile available on different ten apps or websites. Apart from it there should be a partner panel on our app, so that when user submit details of their mobile to sell on our app then its lead should go to all the used mobile phone purchasers on that pincode. When any partner will receive any lead then partner should have the option to offer any price against that mobile phone, if customer like the offer or not then they can accept or make counter offer or decline the offer. If customer like the offer then they will accept the offer and as a result, an amount of 100 INR will be deducted from Paytm wallet or debited card of our partner not from seller. After payment is deducted from partner. account, google map location of buyer will be shared with that partner. Service will be free for mobile seller but will be chargeible for buyer. If amount is debited from the account of partner, then mobile seller contact details should be shared on partner's panel on our app. There should be a web admin panel where customer and partners will be connected and web admin panel should have all the rights to control both. Admin should have the rights see all the sales history of our app, admin can see the sales history of any partner. After deal is done between customer and partner, customer should get the review and rating feature to be posted on the profile of that partner. Deal will be considered closed after entering an OTP shared with customer. That OTP will be shared to customer after service charge deducted from partner's account and credited in our account.