Any tricks or tips for selling things on local marketplaces?

Fuck haggling. I set a lower price because I want something in good condition gone and would rather it be used than go to landfill. Set a price and that’s it. People want to haggle on marketplaces because they either have nothing better to do or resell. Don’t be a party to it imo. Makes it much easier because you ignore tyre kickers who obviously don’t read as well.
- Jesus, this is me. I wish people would just tell me the price, and I could trust that they're not just trying to haggle, or stiff me. I always just start with what I'll accept.
  We got new doors on the house this year, and it took me a while to get around to putting the "No Soliciting" sign up. Immediately started getting door-to-door sales. One does this spiel:
  Him: "Normally, the initial cost is the big one, $600, because we have to bring out the truck, but we're in the neighborhood doing all of your neighbors so we can take off $300."
  Me: "No thanks, I'm not interested."
  Him: "I really want to win your business, so I'll take off another $100."
  Me: "No thanks, I'm not interested."
  Him: "I don't know if you look at Google reviews, but we're number 1! And, look, I really want your business, so I'll take off another $100!”
  And I'm thinking, "so, what you're telling me is that you jacked up a fake up-front cost for suckers to use in the sales pitch," and it's having the opposite effect on me. The more he's "knocking off" cost, the more it feels like he's running a scam.
  It's one of the things I hate most about capitalism: the behaviors and lying it encouraged.
- I keep forgetting i dont usually haggle so much these days once I've realized what I value things at. Thanks

Like the other comment said, think of the actual price you want to sell, then add a bit more. So when people haggle, you can bring it back down to the price you actually want. If I want to sell an item for $50, I post it as $60-$65.
- To add to this, I often calculate shipping ahead of time, add $3-$4 to it, and roll it into the price and charge no shipping. The clarity of price on the front end seems to make a difference And when I add a couple of extra dollars it protects me from surprises
- I kinda want to add $100 to my "purchase price", 1/2 it, and add like $25 to haggle down from
  
  That's some weird math that may not scale correctly.
  
  Use a percentage, like 15% higher or 25% higher. That will scale better with cheap or expensive items.

I always start with the price that I would want to pay if I were looking at/searching for that item at that quality. And that's the damned price, no haggling. I will lower the price unbidden of the person is super chill and easy to work with. Sometimes I just give it to them when they show up.
Because here's one of common use cases of selling stuff: you're not using it anymore, so you're selling it to recoup some of the investment, right? Otherwise, it is taking up space, consuming your resources, and providing you negative return on value. It's a millstone for you at this point and any dollar amount is recouping your finite life capacity, to which no dollar value can be assigned.
Yeah, I know there are plenty of other cases... maybe you're trying to afford an upgrade or afford something else; that's a whole different issue. Also scalpers and resellers. Fuck those parasites in their ears. My fair-pricing idea can be chum in the water for resellers. Know your customer and don't do business with these assholes. Once you've dealt with your first reseller, you quickly get a read on these bottom feeders.
- I don't know why, but people want to haggle in situations like this. Setting the price and being firm may not move the product as fast as a higher price and haggling.

Write down your current minimum, stick to it. You can review after a few days if there’s no interest.
Be up front, show pictures of flaws or damage on the items.
Respect people’s time. Keep the listing up to date. Try to learn from failed interactions and update the listing accordingly.
Have an idea of how the item is getting to the buyer and how much that would cost. Prefer to meet in person in a well trafficked area when others will be around and there are cameras nearby that you can rely on in case of robbery. Inside a Starbucks, for example. If someone is resistant to meeting in a public place, reconsider doing business with them.
Cash is king. Everything else can be clawed back if they scream “fraud!” Having flaws on the listing will give you a lot of power when someone tries to get the money back.

Whatever you think is a fair price. Double it. Then negotiate down.
Say you're open to negotiate. If you're firm about the price and add shit like "I know what I got" you won't even get an offer because people will just assume you're an asshole and won't want to deal with you.
Post the price. "If you have to ask, you can't afford it" holds true most of the time.

Be sure to price a used item for less than it retails new. The number of times I see something for sale on Craigslist, Offerup, ebay, etc and then just do a quick google shopping result and see if for significantly cheaper new is too many.

Look at a sale price for something similar. I was looking at used car seats and someone was pricing a used at the sale price of a new.

Meet in public for expensive transactions.

exactly, add $20 then when they try to get $20 off everyone “wins”