I think alot of the higher than retail prices relate to the extra mags and aftermarket components that have been added. At the same time just the knowledge that you could buy a brand new one for alot less and do the dress up yourself would make it very difficult to buy one on here. Sometimes you just have to eat that extra cost when selling. Just like anything else.
Or part it out and sell everything seperate. I have pulled accessories and sold them that way, it takes longer but you will recoup more of your money. The add-ons don't hold their value, like the firearms themselves do.
I personally enjoy though when certain dealers offer outrageous prices on their guns. Like a Century C93 for around $700 or an AMD-65 for over $700. You can find them way cheaper on Gunbroker, Aimsurplus, J&G Guns, etc. etc..........