Everyone thinks of this differently. As for me, I’ve done a lot of buying and selling online. My F.S. listings are always priced rationally, and sometimes quite aggressively (unlike some that are just 10%-15% under list price, which is silly). My my listings always say, "Please, no lowballs."
But of course lowballs pop up. The real reason is dedicated lowballers put out dozens of offers. Not a single offer is serious--usually they say little other than "will you take $xx?"--I have to assume the theory is every now & then the lowball will trigger a seller's desperation; then the lowballer can then flip & profit from the item.
I never give lowball offers to sellers and just don’t want to deal with them when I'm the seller. To my way of thinking, they’re just drive-by opportunists, the opposite of serious buyers.