There are good answers and if you are still looking for alternatives:
Step 1: Display Customer and allow the user to Skip or Select
Step 2: Display Item and allow the user to Skip or Select
Order of display is purely driven by the context and that will also influence the usability.
Displaying one after the other keeps the Cognitive load to the minimal with no choices to make.
To keep the user NOT guessing, the second option could be displayed as grayed out but transparent (similar to how modal windows are expected to allow the user to allow user to still retain the view of the underlying screen content).
Hope this helps.