The rating is not done by Agora.

One of the posters or lurkers gave you a negative rating as they thought your post wasn't worthy of interest or something to that effect.

Please take note on the negative amounts for a few who post. Many of their messages are given a negative vote almost immediately after posting the message.

I think someone or a few have it in for a few posters. JMHO

Regardless, the good message end up with many positive votes and that tells others that the post has value.

The system is flawed, but has merit.