Car Purchase App & Desktop Tool

I need a seamless way for individual car buyers to handle every step of a purchase—from the first offer to the final paperwork—without ever setting foot in a dealership. The project has two parts that must work together:

• Buyer-facing mobile app (iOS and Android): lets users submit offers on listed vehicles, negotiate in real time with the seller, receive counter-offers, and move straight into contract and finance paperwork once a deal is reached. Secure document upload, e-signature, and push notifications for each negotiation round are essential.

• Companion desktop or web program: stores all listing, offer, and contract data; synchronises in real time with the app; and gives me clear dashboards for tracking buyer activity, completed deals, and document status. A clean export to CSV/Excel for accounting is important.

Deliverables
1. Production-ready mobile app with source code and test flight/Play Store builds
2. Desktop/web program with installer or deploy script and full database schema
3. REST or GraphQL API that keeps both sides in sync, fully documented
4. Brief user guide plus technical documentation for future maintenance

Acceptance criteria
– A buyer can create an offer, receive a seller response, counter, and finalise terms in under five steps
– All signed documents are stored and viewable on both platforms immediately after completion
– Data remains consistent across devices after network interruptions

I am open on the tech stack—React Native, Flutter, Swift/Kotlin, .NET, Electron, or similar—as long as it’s reliable, secure, and easy for me to maintain. Please outline your proposed architecture, timeline, and any past projects that show you’ve built transaction-heavy apps before.