Pretty much everything that involves some sort of "authority" or "power" can be misused. You should intuitively come to this conclusion.
Between you guys didn't confirm if there is some appeal or rating review mechanism?
No. First you take it up to the person who gave you the rating. If they do not respond or ignore you, then you can ask the community. If the community agrees that the rating is unjust, then you can contact the relevant DT1 member. If the allegedly unjust rating was left by a DT1 member, then you need to contact theymos.
Do negative ratings by Jr. Members and below even matter? I have two negative ratings by spam accounts but it doesnt seem to have a negative effect at all.