I don't think it's right as soon as someone posts an ad up that people come in to say it's not worth that.
Even if it's true the seller has a right to ask what he wants for it.
Some people are happy to wait to get what they want.
I think you should only be allowed to pm the seller to advise him on his pricing.
or report the seller if you think the price is grossly disproportionate and he is just trying to rip someone off.