You can't delete a customer, but you can make them inactive. Once inactive, the customer no longer appears on reports, on the Customers page, or in the customer index in the split view.
This is safe to do, because you can always make the customer active later. And if you need to, you can change a setting to display inactive customers on the Customers page or customer index.
To make a customer inactive:
Note: if the customer has a non-zero balance, QuickBooks will ask if you want to make an adjusting transaction to remove their balance.
You can select a setting so that inactive customers are listed on the Customers page and in the customer index.
To display inactive customers:
In the navigation bar, click Customers.
Inactive customers aren't included in reports, but they are included when you print the Customers page from the print icon above the table.