Wanting make shop system, how can I disable this condition after item sold?

Hello guys, I have a problem with this script. I made a buy button to buy something. It works but I want to make this system not working after I clicked once. Here is my script, I received Index value to choose which item is selected. I want to make this into these if statements. I tried to make with bool but I couldn't. How can I do that?

Thank you!

 public void BuyButton()
 {
     switch (index)
     {
         case 0:
             if (//Item has not sold)
             {
                 moneyAmount -= firstMoneyOfRocket;
                 PlayerPrefs.SetFloat("Cash", moneyAmount);
             }
             else if (//Item sold)
             {
                 Debug.Log("You already bought this item.");
             }
             break;
         case 1:
             if(//Item hasnt sold)
             {
                 moneyAmount -= secondMoneyOfRocket;
                 PlayerPrefs.SetFloat("Cash", moneyAmount);
             }
             else if (//ItemSold)
             {
                 Debug.Log("You already bought this item.");
             }
             break;
     }
 }