Once the lens has the dealers mark up wacked on you'd be right. Probably doubles the Â£410 as a minimum. But a reputable reseller would be expected to offer a warranty period and I would hazard a guess that they buy insurance to cover it. Then again most shops have masses of used kit that just sits there, not selling - which is money not working.
But it is annoying. Especially as I have always been very careful with my kit, keeping all the boxes, instructions etc and barring accidents making sure I never put a mark on them.