I think a lot of the return process is automated after they scan the bar code and the product. At least it seems to be the couple of times I have done a return.
I would agree with dana though that if it was part of a cc or ecb deal then I wouldnt return it unless I was willing to surrender whatever bonus I got too. Usually I end up just giving away product that I dont want/ like since likely they were free or close to free. I generally only do returns if a deal doesnt go as advertised and the store staff cant figure out a way to make the deal right.
Most of my returns at CVS are clearance items not ringing up correctly. I would watch better but most stores around here have approximately nine square inches of counter space so I am unloading the cart whilst the items are scanned.