Suppose that depends on your process.
Screen printers may let a customer see the strike off, the first printed shirt for approval before mass production begins.
They could be wanting a design proof to ensure the design is what they want.
They could also just be wanting a one-off/sample shirt, which is easily doable for
DTG and heat transfer, unlike screen printing where lots of preparation goes into setting up the first shirt, but all consecutive shirts are a lot quicker.
If you've gotten a deposit (which you should've gotten at least 50% of the job up front, if not 100%), you're probably safe providing any of the above. Be careful what kind of graphic files you send to the customer if you were the one who designed it, some may go for the cheaper dollar on the reorder without you knowing it.
proof print 
