As annoying as they are, low-ball offers can be ok. First and foremost, don't take much of the sellers time, just a simple "I'm willing to pay $X, if at some point you decide to go that low give me a call". Sometimes starting prices are way too high.
I tend to go with this approach. I bought a Subaru Forester once that was listed for $2700 (it was definitely listed too high based on the condition). When I went to check it out it had a bunch of rust along the sides of the windshield that wasn't visible in the pictures to the point that the windshield leaked slightly and there was a good amount of serpentine belt squealing coming from somewhere.
The guy said his bottom line was something like $2200. I wasn't that super excited about the car based on its condition (it also needed some serious interior cleaning) so I told him I wasn't trying to be a dick or low ball him but the most I was comfortable paying was $1500 so if the car didn't sell in a couple of weeks and he was willing to take that to give me a call. I made it about 3 minutes down the road and he called me and said he would do $1500.
If you aren't comfortable paying what the seller wants I don't see a problem with letting them know what you would pay as long as it is done respectfully and with the mindset/attitude that the seller will probably say no and that's OK. But don't poke holes in somebody's car/truck and then try to low ball them!
For cheaper items (under $100) if I feel something is fairly priced I don't even try haggle. Yeah I could probably get it for $10 less but sometimes its nice to just verify everything is good, hand over the money and be on my way.
Last fall I was selling a good running el-cheapo commuter car and had an 18 year old offer just over 1/2 of my asking price of $1100 (He offered $600, site unseen). He then threw a hissy fit after I declined his offer because I used the term "low ball" and he was offended by that
This really annoys me. At least come look at the item. When I get those super low ball texts the only response I send it "No".