What you are running into may itself be a negotiating tactic. Acting as though you wouldn't consider and are insulted for having received such a "low ball offer" may just be another way of asking you or suggesting that you should increase your offer. Make whatever offer you feel comfortable with and it the seller doesn't like it you don't make the deal. The smart seller would try to negotiate but not all sellers feel the same.
Why do so many sellers take offense to offers on their listings?
If you have the 'offer' feature activated then what's the problem with any offer. Comments like 'lowball' offers will be ignored just gives me a bad vibe. If your item has been up for sale then there is no insulting offer. I've made deals with people starting far apart and coming together. If you haven't noticed the audio market seems to have come to a standstill. Any opinions?