No set definitions. If the seller indicates that they are firm on the price, I believe that the only negotiation area is shipping. If nothing is said about being firm on the price, but there is no "or best offer" clause next to the price, I would say that anything below 90% of the asking price is low balling. If there is an obo clause (then the seller can't be firm), I believe low balling is an offer that is less than 80% of the "blue book" or market value. That could go to two-thirds if the item has been for sale for at least three months and the seller invites best offers (obo) in the listing. Gets complicated, doesn't it?
