Apple forced me to accept the wrong phone

I went on to the Apple Store to fix my iPhone 6 and they told me it was likely that they can't fix it. I then decided to by a new iPhone. I asked for an iPhone 6s but the guy at the store brought and iPhone 6 and started to unpackage it. I told him that I asked for an iPhone 6s but he said I had to pay 10% of the iPhone 6 since he already unpackaged it. He refused to give me the iPhone 6s unless I paid 10% of the iPhone 6. I'm soo disappointed because I am a dedicated Mac user. Now I'm stuck with an iPhone 6 I didn't ask for because of the guys mistake. I mean when there is an error on the suppliers side, I think they should take responsibility, not pass it on to the consumer.