If an item is listed as "or best offer" and I'm not quite willing (or able) to do the asking price then I'll make an offer. I usually tell the seller if he does some more price drops and gets to that number then let me know. I think that's pretty fair. The ball is in the seller's court and it's up to him to decide. But if the price is firm I think it's pretty lame to low-ball. It's just wasting everyone's time.