I saw a knife at an antique mall and it looks like a 1962-1966 Vietnam pilots knife. I think it had 3 lines on the riscotto and the blade had factory machined ribbing on the blade. What is a fair price for this and the only way it made 5” was to measure from the tip to behind the hilt/hand guard. Then it was exactly 5”. Is this how to measure this knife? Btw it fit the metal reinforced sheath perfect. He wanted $200. I offered $150. Thanks in advance.