I know why I might do that. If I see a bike that I would only pay $150 and the ad said $200, I might email them and tell them that if the bike is in the condition it is described/looked in the ad, I would pay $150. I would not want to ride 25 miles on my bike to look at a bike just so the seller says, "No, the price is firm". Why waste my time and the seller's time? Sure, the seller might get $200, but that is not what I am willing to pay for it. If the seller says that she will accept $150, then I will go look at it.