We had a discussion thread on this topic going before, and someone there posted a GREAT response to give to sellers who threaten to destroy goods unless they are paid a certain amount:
"I'm willing to offer you $200 for the Amiga computers. If you refuse to accept this offer the MONEY WILL BE DESTROYED!"
...of course, you insert whatever money amount you are willing to spend. Hopefully reading an insane statement like this will make them realise how idiotic they are being.
Otherwise it's just hilarious!
In my own experience, I had a guy who beat me to the punch on the local Freecycle list - he got an Amiga 500 and peripherals for free from a generous person. He took them just to just see what they were (he didn't know anything about the Amiga). He got bored with them a few days later (probably when he realised they wouldn't run Windows) and he offered to sell me the parts (which we BOTH knew he had just gotten for FREE) or he would fire them in the trash. He refused to pass them on for free - when I was probably the only true Amiga user in my smallish town. Now, you can say that he was within his rights, but in my opinion that's being a Class A schmuck.