I'm a firm believer of haggling on just about everything I buy on Craigslist/ forums, except for services.
Cars/trucks, log splitters, saws, guns, ammo... absolutely there's no harm in trying to save yourself a couple of bucks. But what you can't do is be an ******** about it.
I've sold over 140k worth of stuff on Craigslist over the years, boats, box trucks, dump trucks, cars, atv's you Name it I've probably sold it. I think I didn't haggle on price with ~5 items. Everything else was listed with some type of wiggle room. If I wanted $600 I'd post it for $700. That's the nature of the beast.
I've low balled a few times....I went to check out a 91 f350 stake body dump truck that was listed for $5500. I had $5500 plus tax and tag money with me. Went to check the truck out, it needed a ton of stuff, right around $2500 worth of repairs, tires, brakes, dump piston leaked, rust holes in the floor etc... The market was soft at the time and it was the beginning of winter. (Worst time to sell a dump truck) I told him thanks for your time I wasn't interested, turned and started walking. He said make me an offer. I declined because I was going to offer him $2,000 and didn't want to insult him. He says to me as I get in my truck, I'd consider $3,000. I told him I was thinking $2,000. He said I can't do $2,000 I said I'd do $2,250 as I started my truck. He said follow me to the tag place.
I got the truck for $2250 just for asking, literally half price. I fixed it up and sold it mid spring ( best time to sell a dump truck) for $5700. I intended on keeping the truck but the electric over Hydraulic hoist was too lame to dump a couple of loads I had in it. I was upfront with the issue and a mulch yard bought it from me.