This is not right..

It might be that common decency and manners can vary a L O T from person to person.
I've sold things with the help of this site. Sometimes with a high demand item, I wish that I had one for every person that responded....Not because of the money but because I know that it sucks to want something and miss out on it.
I always respond to the messages in the order that they come in. I tell the first person that they were the first up. I then respond to the others that I have others ahead of them and that if the deal falls through, I will contact them.
That is how I want to be treated. It has worked out well for me.