I have no problem paying 1/2-3/4 full price for top quality gear, depending on age and condition. The seller recoups a fair amount of their money & I save a fair amount of mine. In some cases it's a nicely put together set-up that would take extra money & time to put together. If someone is just getting into this sport, it's a good way to get started. The problem I see with many of these ads it that they expect to recoup ALL of their money for stuff that's 2-5 years old. Yes, maybe it's top notch stuff in excellent condition, but asking 100% full price is silly. The other problem I've seen it folks asking MORE than full price for low end stuff. In these cases (like the Sea Eagle ad), I think they don't have a clue what full market price is, and they just guess at what sounds good to them.
My 2 cents. I do scratch my head at these ads sometimes. I know money is tight for folks, and selling "toys" is something that has to be done to make ends meet. I'm often sad when I see people selling their stuff because they have to in order to pay bills, and not because they no longer use the stuff. That sucks.