Question about Trade-In with Best Buy

My carrier is verizon, so Best Buys deal is better regardless ($31/month vs $40) but because I have a trade in I had to go into the store to pre-order.

So I went and was talking to the guy and he had no clue what I was talking about and didn't understand that I was upgrading my current phone and trading in another to get an even cheaper price. The phone I want to trade in is the Galaxy S6 Edge, so that should discount the price between $240 and $336 since the phone is in good condition. I showed him that and he still didn't really understand. He kept saying that it was just a bill credit, which it says in the fine print. But I think I finally explained it to him and he says to bring it when I pick up the phone or just bring it to verizon and they can do it.

Did I get screwed or am I the one just not understanding what's going on? I would like that $18/month payment haha

Edit: Side question, does anyone know the limits Samsung has for pre-order gifts. I know a lot of people that got screwed when order the S8/S8+ because certain carriers/stores shipped early and by the actual release date, they were out