As I see it, the seller is leaving a response email or phone number, and often his or her name; honest or dumb or whatever, they have effectively put their name and reputation on it.
People don't do that all that much here. You pretty much just always reply to the standard CL email. Maybe it's a regional thing.
EDIT: And I'm not sure how this turned into being all about RE: Ads whining about price, but that's not what I was trying to inquire about. What I did for example, was pointing out actual lying and deception by a seller who knows exactly what they were selling.