I know how to read retail tags. However, If I am there to shop, I am not there to work. I will look at the tag, and unless I am exceptionally dubious, I will not match UPCs, so much as description. If your clerk slapped 40 of the wrong item in this slot, I will pay what it is marked as. If someone put one down there, I will not... I understand the difference.
I would have done what you did Jerseygirl. Only, I'd have stopped at the CS desk on my way out.
Scrabb, your right, businesses are under constraints... but what would have taken 5 min, even at $10/hr instead lost them $150 sale. Their economic position will not get better without better care.