I have the opportunity to trade an item locally for this optic. The item that I'm trading is a coke machine that I converted into a gun safe/cabinet. I feel the value of the safe is between $300-$400. I used the Hide search and came up with some old classified ads. It looked like most of them went for $450 or so. I guess my questions are: Are these worth $400 lightly used? What to look out for, as far as knock offs?