Interesting thread, reading everyones' views on negotiation. I sell a lot, not because I'm in the business or trying to make a profit, but because I like to try new things and have to sell stuff to finance the purchase.
Some people say you shouldn't get offended at low-ball offers. I've been offended many times, and usually just ignore the offer. Nothing wrong with making an offer, but my rule of thumb lately is to ask if the price is firm, or if they have room to move. Most sellers won't have an issue with that.
Often if an item is priced fairly, I won't even bother asking. Just went to a show last weekend and a gentleman had a table full of boxed rolling stock for $15/each. No need to negotiate that! :-)
