Sorry for the novel: but I like to talk about this stuff...
I look at a lot of stuff but I walk away from a lot of stuff, but some rules that have helped me get some okay deals are these:
1.) I think it's a good idea to develop a little back and forth with a seller before I would ask if they are negotiable and try to flesh out how negotiable they are before I ask to see the thing. I tend to ask a buyer about themselves and about how the thing worked the last time they used it.
I rarely make offers over the phone unless it's a long drive.
2.) a.) NEVER NO CALL NO SHOW: don't skip an appointment made without plenty of notice and ALWAYS be on time: nothing annoys me more than a buyer who doesn't show up or shows up super late. We're all busy. Being on time reinforces that their time is valuable and my time is just as valuable as theirs.
b.) Don't show up without a vehicle that can transport the thing you're looking at. If you're a serious buyer and want a deal, show up with a truck to drag said junk home or a second person too so you can drive your new junk home.
3.) Know what you're looking at. Do your research. Don't poke holes in people's stuff (figuratively and literally)> I try to feel out if someone will be offended if I mention what I think is wrong before I tell folks: most people know if their junk needs work and it's not polite to list everything.
4.) Use comparisons at your own peril: nobody likes to be told their stuff is crappy and most people attach value to things as they value themselves. (That's why your little sister got mad at you when you told her the band she liked in high school wasn't cool: you're not telling her she isn't cool> but that's what she hears).
5.) I like to use contrast: if I like the thing I'm looking at I don't hesitate to compliment it, then if there's a problem it doesn't sting if I mention it.
6.) Make a realistic offer and stick to it. If it's not worth what they're asking and they don't want to sell it for what you feel is fair then it's not the thing for you. Again be respectful and thank them for their time. Being a gracious buyer is much easier than being a gracious Non-buyer.
Selling:
1.) I don't mind low balls- it comes with the territory, but I don't mind telling people NO and if they're weird on the phone- I don't let them look.
2.) I totally echo what everyone else has said: I list at them middle upper of the price range:
(If it warrants it)
I don't like to sell garbage, if it's junky I usually fix it or list the problems up front, no one likes dishonesty.
3.) I really liked what you guys have said about setting a higher price and letting folk "haggle me down" to a number I'm ok with. That's an interesting idea.
4.) Value for Value: (notice I didn't say win-win). Most deals are lopsided to some extent, what's important is that the buyer and the seller both feel they are getting value for what they put their cash up for. Remind your potential buyer what value they are getting, never beg for a sale - You've got more respect for yourself than that.
5.) Have your paperwork ready, don't waste people's time looking for a title or some napkin to write a bill of sale.
I bring a bill of sale and a working pen with me when I buy stuff, so I'm not standing in a field while Bubba asks his wife for a pen that works.
6.) a.) Be a gracious seller, if you've got the time: help people load up or at least give them pointers, I've had people shy away from buying a motorcycle before because they weren't sure how to load it: a quick hand and they became serious buyers.
b.) Don't promise them the world, and make your terms known for example, "I'm selling this as is" wards off buyers who call back and piss and moan about a scratch you didn't disclose to them on a 50 year old Jeep.