Uhmmmm...you paid $500 and you want $500? Good luck. See, it is kind of like a used car. You may only drive it off the lot, but it is still used.
Sure, you say your marker has never been shot and I'm not calling you a lier...however if someone gets this and has a problem with it they can't take it back to the shop or mail it back to the store they got it from. They are stuck with it. That there is a valuable piece of mind.
Not trying to be negative...but you may have to rethink your stand on this...or try e-bay.