You do the trade in's via the mail and you are sent a gift card to use. The store has nothing to do with this program. I would try and sell though other means. I am sure you can get a couple more bucks and it will be in good ol greenbacks.
I have been looking for this question and answer up until about the 10th page. All I kept seeing were the same questions and answers. So anyway, I want to upgrade to the HTC Thunderbolt, I have the Droid Incredible. The appraisal on it was 100$. What happens to this phone if I go the store and upgrade? Will they take it in and give me 100$ credit?...Or do I just need to sell my Incredible to a friend or something. I paid the discount price for it when I started my first Verizon contract.
Thank you for searching for your answer first! Most people just post the same question that's been answered two posts down... Anywho... As the other poster said, I would sell your Dinc through other means. Verizon's trade-in program gives very low values for phones that you could get 3-4 times as much selling on eBay or Craigslist. For example, my perfect condition EnV3 was quoted at $12, I've seen some on Craigslist for over $100. So yeah, I would purchase your Thunderbolt, and then put your Dinc for sale online or to a friend or something for much more.
Don't forget to factory reset the old phone if you decide to sell it. Format the sd card too if that is going with the phone.