I grew up where haggling and "wheeling and dealing" were a way of life. I sell a lot of things online and I don't mind a little back and forth with a prospective customer if they are polite and respectful. If you're offering me less than 50% of my listed price I'll let you know (in the kindest way possible) that you can go rapidly fornicate with yourself. And I'll never respond directly to the question: "what's the lowest you'll take?" I'm not bidding against myself.
Conversely, if there's something I want, I have no problem tendering a respectful offer. Especially if the item has been sitting awhile, or doesn't seem to be garnering much interest. Ie: the day before an ad on here is set to expire. But I'll add that I'm pretty much "just shooting my shot" and if they won't accept my offer, no harm: we can keep talking.
The key takeaway, I feel, is that respectful offer. I try to ask myself how I'd feel about my offer, if the rules are reversed. So, if I were making an offer on a Hi-Point, I might offer a box of ammo less than asking price. If I were making an offer on a $3k+ 2011, I might offer a Hi-Point less than asking price.