GAAP Applications-Internal Control - Discussion

The following is an excerpt from a conversation between the store manager of Brothers Grocery Stores, Lori Colburn, and Terry Whipple, president of Yoder Brothers Grocery Stores.

Terry: Lori, I'm concerned about this new scanning system.
Lori: What's the problem?
Terry: Well, how do we know the clerks are ringing up all the merchandise?
Lori: That's one of the strong points about the system. The scanner automatically rings up each item, based on its bar code. We update the prices daily, so we're sure that the sale is rung up for the right price.
Terry: That's not my concern. What keeps a clerk from pretending to scan items and then simply not charging his friends? If his friends were buying 10-15 items, it would be easy for the clerk to pass through several items with his finger over the bar code or just pass the merchandise through the scanner with the wrong side showing. It would look normal for anyone observing. In the old days, we at least could hear the cash register ringing up each sale.
Lori: I see your point.

Suggest ways that Yoder Brothers Grocery Stores could prevent or detect the theft of merchandise as described.