If it was real, that would be a good price. It is a rare collector's item in ammunition collecting circles. Even Uncle Sam doesn't use it much due to cost. Depending on manufacturer, some green tip paint is very dark - almost a translucent blackish green - but it's still just plain old M855.I saw 20 round boxes of black tip 5.56 at the 1500, unsure on the grain. $3/round or so...
PD trade-ins are a thing. Ballistic lab leftovers/excess from testing is also a thing. A couple of years ago, some M993 made it out from a domestic military contractor who had a foreign work contract that got cancelled after they had already legally bought supplies here in the U.S. They didn't have any other work on the horizon, so it was legally sold on the civilian market to recoup costs, but very discreetly. There are lots of small "leaks" where such things can make it into civilian hands legally - it just depends on the contract language that was used when whatever entity bought the stuff got it. American Reloading had TONS of M855A1 projectiles years ago from a pull down contract and went about selling them on the civilian market - Uncle didn't like it and tried to stop it, but a quick lawsuit showed the contract language was clearly in American Reloading's favor and so they were able to continue selling it. Some old timers may remember when "green tip" M855 ammo was treated much the same.I don’t think it’s ever been offered for civilian sale so it’s gonna be hard to say you’re not in possession of stolen gov property.