I am a business owner, and I would never do that to a customer, if they are in the right or in the wrong. A customer should always leave your place of business with warm and fuzzy feelings towards you and their purchase. Even if they can't, they should still do it in a way so you don't feel bad. SO SHAME ON THEM!!!
On another note, I have no problems asking for a deal... I tend to deal with only 2 LFS in my area, and they know I am going to always ask them. I just bought 6 peppermint shrimp, he was selling for $17 each... I asked for my deal, got them for $12 each and the sixth one was free...
This is why I only deal with these 2 LFS, because of their customer service!!!