Yes, they can, it is their shop.
I have been disgusted by shopping at Fry's for Memory. I have given exact specs and seen prices in one part of the store and then been offered something else in another. Like I wanted 1G of DDR3200 in two 512M sticks and the paperwork, when I got it to the register was for one at the price of two. Another time I got DDR2 spec'd on my paperwork when I wanted DDR. The third time was the charm.
Each time, I just took it off my order, but the third time, I left my entire order at the counter and left Fry's never to return.
Their shortsighted policies will show them the door in the business world. They need to train staff better, and they need to improve their own quality.
But for you... Can you honestly work a permanent job where you are unable to believe in the policies? That will be bad for you and bad for them. They have the right to be what they are, and you have the right to find a better job even before they fire you.