There is an option when you place an ad to choose notifications when somebody replies to your ad. A lot of people miss that and by default it was set to NO. So unless you went and checked, you would never know when you got a reply. I assume that most people who place an ad would want to know when they get a reply or question so I changed it to default "YES". So if you DON'T want to receive notifications, you will have to remember to select no when you place an ad. Unfortunately, this change does not affect any ads that are already placed and there is no way to go back and edit it to include notifications if you didn't do so when you placed the ad.
Now for you buyers. The BEST thing to do is to also click on the link in the seller information that says "Contact Seller". I've seen a lot of people post a reply that they want the item but in the meantime, somebody else may have already used the "Contact Seller" link so may have gotten ahead of you. It's OK to post a reply but if you REALLY want to make an attempt to be the first, you should contact the seller.