I have a simple rule. If the offer is less than 80% of the asking price, then I assume it's a lowball and simply ignore it and the offeror.
Some people list at a fair price. If that's what it is I'll not even haggle. like bought a fully CNC taig mini Mill with computer software and 4th axis for $900. Hand cash walk out. Fair price.
Other shit is obviously over priced and so you negotiate.
Sold a lathe recently for $1400. I had firm on the price. Took a year to sell. Sold firm.
It also depends on the product here. Consumer popular shit like games and cars have a lot of negotiation. Some tools. Other shit is less negotiated.
Some shit is high demand and lots of haggling like motorcycles. I just enjoy the hell out of telling people no.
"That offer is offensive and I've setup a block list for you"
I like this strategy.
This seems like inexperience on our side and naive expectation for more reasonable approach, but it really felt borderline rude.
Of course, there are cultures where haggling is the norm so, in these cases, it's best to start with an artificially high price which enables you to keep making concessions until you reach the price you wanted anyways.
That was a good day.
That's not how haggling works. My lowest offer is $500 until I hear yours.
Aside from that, I've had good experiences selling old video game consoles on Gumtree.