Thanks for the insight. No wonder a seller told me "It's an all-match gun. you can inspect outside, but you are not allowed to dry-fire it, nor disassemble it." ...... no dry-firing is understandable. No disassembling, he mentioned that he dared not disassemble it, and not allowing me to disassemble it, all by his grandpa's words "it's all matching" ?? Originally, I thought he worried that I could not put it back "If I cannot put it back, of course I will keep it". No.... he said something like "what if you keep parts"..... My brain still did not turn around.... parts for $2k?
But finally he gave up. It's like selling a house, open-house session is annoying but cannot be skipped.
=====
Just thought a little more. What if I had really found problems inside, e.g. mismatched parts inside, and he insisted it's all matching before he sent to me.... because his grandpa had told him so. That would be a big headache. Well, nothing could go through based on that assumption.
What's missing is an independent 3rd party that both seller and buyer trust to coordinate the transaction.