Welcome to Part 3 of my blog series on building QuantoxBay, a full-stack digital marketplace where anyone can upload and sell digital products and anyone else can buy and instantly download them.

In the previous part, I walked through how I designed the core models Users, Products, and Orders in a way that kept the platform simple, scalable, and role-neutral. Now it’s time to talk about how all of that comes together through the actual logic of the application — what happens when someone uploads a product, makes a purchase, or accesses a download.

Uploading Products as a Seller

On QuantoxBay, any logged-in user can act as a seller by uploading a digital product. I made the experience feel light and creator-focused just a simple form where the user adds a title, description, file (like a PDF, ZIP, or design asset), and a price.

Behind the scenes, the platform automatically links that product to the person who uploaded it. From there, the product becomes visible on the marketplace, and ready to be purchased by anyone.

The goal was to make the platform feel like a creative studio, not a complex dashboard. No vendor verification steps or role switching just build, upload, and sell.

Browsing and Buying Products

Once a product is listed, any visitor can browse through available items. The product pages include clean previews, pricing, file type details, and a “Buy Now” button that kicks off the checkout process.

When a user decides to buy a product, they’re redirected to a secure Stripe Checkout page. After the payment is completed, they’re automatically brought back to QuantoxBay where the system confirms the purchase and unlocks access to the file.

I used Stripe’s backend verification process (webhooks) to make sure that downloads are only made available after successful payment. It’s fast, reliable, and adds a level of trust to the platform.

Controlling Access to Digital Downloads

Access control was one of the most important parts of the logic. I wanted to make sure that users could only download what they actually purchased and that files weren’t publicly exposed or directly accessible.

So after payment is confirmed, the buyer sees a download link on their order history page. From that point on, they can re-download the product at any time. If someone tries to access a file they didn’t pay for, the system blocks the request.

This simple permission logic ensures:

Files are secure and private
Buyers feel confident in the system
Sellers know their work is protected

Personalized Dashboards for Everyone

Each user has their own dashboard no matter whether they’re buying, selling, or doing both.

As a seller, you’ll see the products you’ve uploaded, how many times each one was purchased, and the total revenue generated. As a buyer, you’ll see your order history, purchase dates, and download links.

This shared dashboard approach reinforces the idea that the platform is for creators people who buy and sell, learn and contribute, all in one space. I wanted it to feel like a personal studio space more than a cold marketplace.

Making Logic User-Centric

One of the biggest lessons I learned while building QuantoxBay was that logic isn’t just about code it’s about designing systems that mirror how people actually think and behave.

For example:

Uploading something should be simple and fast, not hidden behind admin tools
Buying should be trustworthy and smooth, with instant access
Dashboards should show what matters to each user, without clutter

That’s how I approached every part of the core logic not just as a developer, but as someone imagining what it’s like to use this platform.

Coming Up Next

In the next part of this series, I’ll talk about how I integrated Stripe into the flow how the platform handles secure payments, ties them to products and users, and ensures that files only unlock after successful checkout.

Thanks again for following along. You can try the live platform here:
quantoxbay.onrender.com
Or explore the full codebase on GitHub:
github.com/vedantmpatil/Quantoxbay

Let me know what you think I’d love to hear your thoughts, feedback, or questions.

See you in Part 4: Stripe Payments and Post-Purchase Experience.

Core Logic and Views – Uploads, Purchase Flow, and Access Control in Django