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

I think the seller, making it clear that he feels no obligation to respond to every low ball offer is just good communication.  if the offer is close enough that he feels it's worth his time to respond then he will.  Nothing personal either way, just good communication that the seller may not deem it worthwhile to respond or counter offer.

I have a process that I follow before and during selling.This is just my opinion.

1. When pricing your item don't look at what sellers listing price.  Look for the "sold or complete" price on all websites to get your base price to list. Many sellers will list a ridiculous price and they think this is what the market pricing is. 

2. Unless the price is firm; I will accept an offer with a 15% and 20% less. This is retail sales standard practice. Some sellers believe that 10% is a great discount, but in my opinion,10% is not an exciting offer to give for items under $500. 

Negotiation is part of the process. I expect offers when I list something. I evaluate supply and demand and determine how much I’m willing to move on offers. When buying, I often make polite offers.

Those who are offended by offers are generally:

1. Control freaks.

2. Likely to keep owning the items listed for sale for a long time.

Jerry

PS  If you have to announce that you will ignore lowball offers then you aren't very good at ignoring...if fact, you have already acknowledged them before they are made and I bet most of the time you will respond to them, probably with a smart ass remark of your own.

@carlsbad I agree with you.