I don't think people are understanding this $650 trade-in correctly (which Verizon hasn't done a good job of explaining).
It's a 2 year device payment plan. If you want the base IP7 32GB ($650), you will be charged $27/month x 24 months and then given a $27/month credit if you trade in an IP6 or IP6S (or the plus models). That's $650 in credits.
However, if you upgrade to the new iPhone 8 next year, your monthly $27 credits will end. You will mail in your iP7 (that's how the 2 year device payment plan works) and you will then start paying $27/mo for the base iP8 (or more depending on the capacity, etc.).
So it's really "up to $650" in credits. You can't expect Verizon to give you $650 for a used/old phone AND give you a free iP7 that you can do whatever you want with without being under a contract. They're not giving you something for nothing.
I'm pretty sure I'm right about this. Sadly, it sounds like Verizon is misguiding a lot of people and many of their reps are uninformed about how this really works and what they should be communicating.