Found this out the hard way unfortunately.
If someone is asking way too much for something, there is no good way of telling them that without feelings getting hurt and a flame war started.
Let the market tell them. They will figure it out when nobody buys it or responds to the ad.
If you want to lowball somebody, you will find that doing so in a PM will cause a lot less trouble on the board.
These are suggestions, I'm not trying to tell anybody what to do - really more like relaying what happened to me in a couple of instances (no, I was not the lowballer ) GG