Dealers use the tax savings to their advantage and usually their trade in offer they give you is less the tax savings. I've found they often offer a little less than the tax savings just because they know there is value in just getting rid of it rather than selling it yourself.

It's always what your time and effort is worth to you. For some, saving $3k and selling it themselves is the obvious answer. For others, losing $10k and getting the deal done that day and moving on with their time is the way to go.

We own pawnshops and I use the same mentality when people want to sell us items. I'm very upfront and show people what they could sell stuff for on ebay, facebook or guntrader. I then explain I need to make money on the deal and in order for it to be worth it this is the price I can pay. 9/10 people take the deal because they don't want to mess with selling it themselves.