Oh this annoys me too but I just think "you don't know if you don't ask" right? I try not to be offended by someone's lowball offer when I'm the seller and I try not to offer too low when I'm the buyer.

I have had people come and do the "will you take this?" and sometimes I say yes and sometimes I say no. Most often, if I say no, they still buy it anyways because they don't want the trip to be for nothing.

I usually mark my prices $5-$10 more than what I want for it so that this allows for negotiations. I get what I want and the buyer thinks they got a deal