Honestly, I don't understand why people get so offended by lowball offers. I suspect it's just the lack of haggling in American culture. I just say "no". Or I negotiate, depending on what I want.
Clearly a lot of people are desperate to sell, and I'll bet lowballs work quite often. They're not going away, either way.
I can get frustrated if someone is pushy, but it's not terribly difficult to ignore.
I also find it shocking that a lot of folks want 90% of the their initial cost. Used is used. Suck it up. That's why buying used is so great. Let the other guy take the depreciation hit. I can generally buy last year's model NOS for 70% -80% of the new price, so "mint-y" is worth less than that to me.
Is like Markedman post, some low baller asks for an outrage low price thinking you're desperate. I have a low tolerance when someone asked for an unreasonable low price.
That's my definition of a low-baller when they asks for an unreasonable low price then they make some reason behind it like they saw the same item for cheaper. They think you are an idiot.
I don't mind someone trying to haggle down the price of something I'm selling but asking for a ridiculous price from the get go. I think it reflects their personality once they asks for a ridiculous low price. I don't want to sell anything to them.
So I'm not sure what your definition of low-baller. Haggling down the price if fine. That I don't mind.