Welcome to the Community. I can share some information about assigning service items to customers & vendors in QuickBooks Desktop.
Currently, assigning service items to customers & vendors in QuickBooks Desktop isn't available. You'll need to select each item manually upon creating a sales transactions. However, you can turn on the Automatically Recall Last Transaction for this Name option. This will allow QuickBooks to remember the information that you've selected for the previous transaction and automatically fill it in on the next.
Click on Edit.
Select on Preferences.
Click on General category.
Refer to the MyPreferences tab.
Select on Automaticallyrecalllasttransactionforthisname. Click on OK.
Also, I'd suggest sharing this idea to our Product Developers. This way we'll be able to evaluate those features that need to be added in future updates. By doing this can also help us to asses on how we can help you run your business easier.
You can do that by following these steps:
Click the Help menu bar.
Scroll down to Send Feedback Online.
Select Product Suggestion.
Choose Product Suggestion for the Type of Feedback.
Product Area is optional.
Enter your suggestion.
Click Send Feedback.
Please let me know if you need further assistance with your QuickBooks account. I'm here to help you out whenever you needed me. Have a great day!