I think it depends on how low the balls are.
If I list an item and get some insanely stupid offer I ignore it. If the offer is 1/2 my ask and the buyer gives some justification why his # is what it is (ie: "The Audiogon blue book says...." ) I'm encouraged that the buyer is both real and educated. I can work with that.
Some listings are a joke. When some egocentric Malthusian lists his 20 year old worn out amp for what it retailed for 20 years ago it's nearly useless to negotiate. He's seeking validation and not a sale. These types get all huffy when you offer a real world FMV.
Interestingly, an appraiser told me once that an item that sells at an auction is worth the second highest bid. Considering that a bit it made perfect sense.
Assuming properly exposed to the market, in the end an item is worth what someone will pay for it.