I think most dealers gear is hit or miss on used purchase prices, its only normal, they have to take it in and make it worth there while. I watch paw stars (which i hear is fixed) and cringe, "why didn't they just leave and sell it on ebay or CL" and "Wow there is a lot of civil war guns in the dessert and other rare $&#*"
I recently sold a 24-70mm f/2.8 L to cameta camera, my local camera dealer, i was purchasing some new gear, i had a number in my head as rock bottom on CL I would accept, they offered me a fair price, i can't remember exactly but was happy. I got some real low ball offers on CL. I was happy with the deal and put as a discount for funds I was already planning to allocate towards new gear. There was a guy at the same time selling a 17-55mm and a 7d and got offered a really low deal, i was shocked, even if the 7d sells low used market today, they 17-55mm is a solid lens i assumed held its value. I think the combo offer was lower than what i got for the used 24-70mm, cameta sells used gear but also is a huge ebay vendor, they price used stuff very well and pay good prices.
I always try CL and usually make more with ebay but hate the hassel, although with paypal payment popping up at local stores I may reconsider.
Do a test list of a 5d mark II or 7d, and you will see CL or at least the used market is very dead. Fredmiranda seems to be a good outlet but i never used them.
I posted a 7d and got several offers from $400-$600, I know have a backup body