Yeah, it would be hard, but I would probably correct him right away. After all, he's a new guy.
When I bought my first computer at a local comp store, I ordered the "sound blaster live upgrade" with it for $70 (they were expensive back then). The computer had it in there, but it wasn't on my invoice. So, when it came time to pay, I said "The live card insn't on my invoice." So he totalled up the invoice again and said, "Yep, it's all there." I said again, "No, it totalled fine because you didn't add the live card first. " And he said, "Looks right to me." His manager was standing right next to him. Both of them were clueless. I said, "Ok, have a nice day." So, I got my first soundblaster live card for free!!!!