Hard to sit by idly while reading through this train wreck!
First of all to this young man, I am fairly certain that every one who has been posting on this thread is considered your senior, therefore try to be respectful and also LISTEN!
Kudos to you to have developed such a passion for fine knives and other hobbies from eras gone by while other juveniles in early teens are into other contemporaneous hobbies which happen to be alien to older folks like me. That said, you are at the disadvantage of being very young therefore you MUST earn the respect of those who are clearly not in your peer group. Your behavior has been anything but!
Lastly, curiosity is a wonderful thing and if you have the zeal for working with your hands, dismantling, fixing and reassembling things, back that trait up by owning your mistake. You clearly voided your inspection courtesy and privilege when you opened up the seller's knife. Whether he misrepresented or not, your decision at that point to go your certain way absolved his liability.
I hope you hear me.