If it was a simple "Thank you for your post", then that contributes close to nothing and shows you're really just posting for the sake of getting gold. Posts like that are what we call "Spam". They do nothing for the original topic poster, and just takes up space.
When replying, try and actually say something relevant to the topic. There's also a minimum length required which makes sense because there is no way you can wrap up constructive criticism or comments within several tiny words.
講話必需詳細, 建設, 并且獨特. 然後您就不會失去金币. =)