As either buyer or seller, never say the word, "no!" As a buyer, make your offer. If the seller declines, smile and walk away. As seller, if the offer is insufficient, smile and say, "I can't sell it for that" and walk away. One monkey don't stop no show! There is no such thing as rare.
Now, as buyer, if you have to have it, pay for it and leave. As seller, if you need the money, sell it.
Remember, if as a buyer you walk and come back later and it's gone, that's on you. If as a seller, you have to pack up your stuff and haul it home, that's on you.
That's reality.
But God, in his infinite wisdom, invented negotiation. So, negotiate. A deal is not a deal unless it's good for everybody. Some deals will work and some won't.
As a buyer, I like to say, "Please allow me to respectfully submit an offer of $xx.xxx for your lovely ___________."
As a seller, I like to reply, "Thank you for your kind and generous offer, but we're still fairly far apart."
Then let nature take it's course.