A PyQt5-based GUI application for calculating selling profits across different marketplaces, taking into account various fees, shipping costs, and seller tiers.

├── MarketplaceApp/
    ├── data/
    │   ├── marketplaces/
    │   │   ├── ebay.json
    │   │   ├── tcgplayer.json
    │   │   └── whatnot.json
    │   └── shipping/
    │       ├── fedex.json
    │       ├── ups.json
    │       └── usps.json
    ├── logs/
    ├── src/
    │   ├── models/
    │   │   ├── __init__.py
    │   │   ├── fee.py
    │   │   ├── marketplace.py
    │   │   └── shipping.py
    │   ├── ui/
    │   │   ├── __init__.py
    │   │   ├── main_window.py
    │   │   ├── marketplace_widget.py
    │   │   ├── product_widget.py
    │   │   ├── results_widget.py
    │   │   └── shipping_widget.py
    │   ├── utils/
    │   │   ├── __init__.py
    │   │   ├── calculator.py
    │   │   ├── config_loader.py
    │   │   └── logger.py
    │   ├── __init__.py
    │   └── main.py
    ├── tests/
    │   ├── __init__.py
    │   ├── test_calculator.py
    │   ├── test_marketplace.py
    │   └── test_shipping.py
    ├── README.md
    └── requirements.txt

• fee.py: Defines fee types (percentage, flat, compound) and calculation logic

  • FeeType: Enum for different fee types
  • FeeApplication: Enum for fee application (per item/order)
  • Fee: Dataclass for fee calculation

• marketplace.py: Marketplace and seller tier structures

  • SellerTier: Dataclass for seller tier information
  • Marketplace: Dataclass for marketplace configuration

• shipping.py: Shipping carrier and rate structures

  • ShippingRate: Dataclass for weight-based rates
  • ShippingService: Dataclass for shipping service options
  • ShippingCarrier: Dataclass for carrier information

• main_window.py: Main application window integrating all components
• marketplace_widget.py: Marketplace and seller tier selection
• product_widget.py: Product details input (price, quantity, cost)
• shipping_widget.py: Shipping carrier and service selection
• results_widget.py: Displays calculation results and fee breakdown

• calculator.py: Core profit calculation logic

  • ProfitCalculator: Handles all fee and profit calculations
  • ProfitCalculationResult: Dataclass for calculation results

• config_loader.py: JSON configuration file handling

  • ConfigLoader: Static methods for loading marketplace and shipping configs

{
    "name": "TCGPlayer",
    "tiers": {
        "marketplace_seller": {
            "name": "Marketplace Seller (Level 1-4 Account)",
            "fees": {
                "marketplace_commission": {
                    "type": "percentage",
                    "value": 10.25,
                    "application": "per_item"
                },
                "processing_fee": {
                    "type": "compound",
                    "percentage": 2.5,
                    "flat_fee": 0.30,
                    "application": "per_order"
                }
            }
        }
    }
}

{
    "name": "USPS",
    "services": {
        "first_class": {
            "name": "First Class Package",
            "weight_limits": {
                "min": 0,
                "max": 16
            },
            "rates": [
                {
                    "weight_up_to": 4,
                    "price": 4.50
                },
                {
                    "weight_up_to": 8,
                    "price": 5.25
                }
            ]
        }
    }
}

1. Install requirements:

pip install -r requirements.txt

2. Create necessary JSON configuration files in data/marketplaces/ and data/shipping/

3. Run the application:

python src/main.py

• ✅ Core data models
• ✅ Fee calculation logic
• ✅ GUI components
• ✅ Configuration loading
• ⏳ Test suite (to be implemented)
• ⏳ Error handling dialogs
• ⏳ Input validation
• ⏳ Save/Load functionality for frequent calculations

1. Add comprehensive error handling and user feedback
2. Implement input validation
3. Add save/load functionality for calculations
4. Create test suite
5. Add support for tax calculations
6. Implement bulk calculation features
7. Add data export functionality