Thanks and happy new year to you too!

Generally the offers from stores suck compared to selling to individuals on a forum/eBay in my opinion. I have asked for a quote only once. It was to upgrade from a 70-200mm f/4L IS to the f/2.8 II version and got a lousy deal. It was like 60-65% of the value of a new lens. I ended up selling the lens for about 85% of the value of a new one (with a filter as a bonus and warranty was still valid for 3 months). My experience is limited though and the only store here in Finland that offers trading in gear (or has an official quote asking form on the web at least) is very expensive anyways, they even ask more for some used L lenses than some online shops for new ones. The low trade-in prices are probably because a store has to pay taxes on the used lens etc. My advice would be to just try to hang on and sell the lens to an individual when someone offers a fair price. I also tend to list shipping expenses when I sell something and ask that the buyer pays them or at least half.