Why do so many sellers take offense to offers on their listings?

I have made plenty of easy deals as well. I’m just surprised at how many put something for sale and nobody buys it yet they get bent out of shape at a lower offer.

If I see an ad and I feel the asking price is out of line, I disregard it.

I have "low balled" auctions on ebay, "not tested" "not working" "sold for parts". Even if they do not state "open to offers", I send them a message. I state the possible problems it may have and cost to repair. Hopefully justifying my low offered gamble. I low balled one Mark Levinson power amp. It was the Seller father’s amplifier, and he knew nothing about it. A gamble purchase for me. I suggested for he to take the unit to a reputable "highend" stereo shop to have it checked out. Limo connections. He might get more money and faster sale if the position or disposition is known. "Who knows. They may give you an offer for it right then and there for it."

I try to price an item low enough to my willing to sell for price so that I attract a buyer. I think 30% over that may keep people from bidding. So I guess a 30% lower than my willing to sell for price offer would be too low a starting point.

I guess it’s a balancing act of close enough to my price without turning away a serious potential buyer, but close enough to my price so an actual deal can be struck.

My 2¢

I price my items according to what others have sold for. If I get an offer that is ridiculous to me, I don’t respond. I’ve gotten ridiculous offers hours after I posted things for sale which I would never accept. It’s not like going to a swap meet! I don’t mind sitting on things for sale for months.
If you go into a car dealer to buy a Porsche, are you going to offer them 50% off? Of course not if the car is in good shape and its price is within kbb limits. Why would buying audio items be any different? It’s not. 

Since this is a used gear site, the art of bargaining and negotiating is in full swing. If I list a unit for, say, $2K, and someone offers $1100. I'm not insulted; I just counter with $1950. That either silences them or they climb the steep hill and offer something closer to the asking price. 

But if I want $2K for my unit, then I'm not going to list it for $2K.