Ellerinize sağlık. Arayüzü biraz toparladım ve komisyon oranı açılışta otomatik 4.99 gelecek şekilde düzenledim.
İlham olması açısından:

import tkinter as tk
from tkinter import ttk

def calculate_commission():
try:
product_price = float(entry_product_price.get())
commission_rate = float(entry_commission_rate.get()) / 100
        service_fee = float(entry_service_fee.get())

commission_fee = product_price * commission_rate
vat = (commission_fee + service_fee) * 0.20
        total_deductions = commission_fee + service_fee + vat
net_amount = product_price - total_deductions

label_commission_fee.config(text=f"Komisyon Bedeli: {commission_fee:.2f}₺")
label_service_fee_result.config(text=f"Hizmet Bedeli: {service_fee:.2f}₺")
label_vat.config(text=f"KDV: {vat:.2f}₺")
label_net_amount.config(text=f"Net Tutar: {net_amount:.2f}₺")
except ValueError:
label_commission_fee.config(text="Lütfen geçerli bir değer girin.")
label_service_fee_result.config(text="")
label_vat.config(text="")
label_net_amount.config(text="")

root = tk.Tk()
root.title("Shopier Komisyon Hesaplama Modülü")

# Stil Ayarları
style = ttk.Style(root)
style.theme_use('clam')

# Grid yapılandırması
root.columnconfigure(0, weight=1)
root.columnconfigure(1, weight=1)
root.rowconfigure(0, weight=1)
root.rowconfigure(1, weight=1)
root.rowconfigure(2, weight=1)
root.rowconfigure(3, weight=1)
root.rowconfigure(4, weight=1)
root.rowconfigure(5, weight=1)
root.rowconfigure(6, weight=1)
root.rowconfigure(7, weight=1)

# Ürün Fiyatı Girişi
label_product_price = ttk.Label(root, text="Ürün Fiyatı (₺):")
label_product_price.grid(row=0, column=0, padx=10, pady=10, sticky="W")

entry_product_price = ttk.Entry(root)
entry_product_price.grid(row=0, column=1, padx=10, pady=10, sticky="EW")

# Komisyon Oranı Girişi
label_commission_rate = ttk.Label(root, text="Komisyon Oranı (%):")
label_commission_rate.grid(row=1, column=0, padx=10, pady=10, sticky="W")

entry_commission_rate = ttk.Entry(root)
entry_commission_rate.grid(row=1, column=1, padx=10, pady=10, sticky="EW")
entry_commission_rate.insert(0, "4.99")  # Varsayılan değer

# Hizmet Bedeli Girişi
label_service_fee = ttk.Label(root, text="Hizmet Bedeli (₺):")
label_service_fee.grid(row=2, column=0, padx=10, pady=10, sticky="W")

entry_service_fee = ttk.Entry(root)
entry_service_fee.grid(row=2, column=1, padx=10, pady=10, sticky="EW")

# Hesapla Butonu
button_calculate = ttk.Button(root, text="Hesapla", command=calculate_commission)
button_calculate.grid(row=3, column=0, columnspan=2, padx=10, pady=10, sticky="EW")

# Sonuçlar
label_commission_fee = ttk.Label(root, text="")
label_commission_fee.grid(row=4, column=0, columnspan=2, padx=10, pady=5, sticky="EW")

label_service_fee_result = ttk.Label(root, text="")
label_service_fee_result.grid(row=5, column=0, columnspan=2, padx=10, pady=5, sticky="EW")

label_vat = ttk.Label(root, text="")
label_vat.grid(row=6, column=0, columnspan=2, padx=10, pady=5, sticky="EW")

label_net_amount = ttk.Label(root, text="")
label_net_amount.grid(row=7, column=0, columnspan=2, padx=10, pady=5, sticky="EW")

root.mainloop()