I look at low ball offers as pretty disrespectful but I doubt those that do so really care. Personally I don't respond because that gives them some attention and I'm not going to even give an inkling of support to their ridiculousness.
Does it make sense to "ignore low ball offers"?
Assuming the person wants to sell the item and is accepting offers (since he didn’t say the "price is firm") then why say "I will gladly ignore low ball offers" ?
Why not make a counteroffer to the low ball offer? Thats how cars, houses and most anything that doesn’t have a "firm" price is purchased.
If its because the seller doesn’t want to waste their time negotiating they should say so or simply grow-up a little bit and not get so easily offended by a low offer. Besides, a buyer has no idea what the seller is willing to accept unless you negotiate it.
I’ve sold and purchased a number items after negotiating from a low first offer.