I've had a similar experience dealing with a guy selling a Singer for $250 here in Australia. I was trying to make him a reasonable offer and he just got all annoyed - it makes sense when you consider they don't care about the machine or the person who wants to use it, they only care about the money. So all they are hearing is "you are not going to get the money you want" and therefore get seriously annoyed.
I just try and tell myself that they might be going through a difficult time at the moment... Or, I suppose if they really do go through life being so rude to people all the time, then they are probably not having an enjoyable life anyway.