- If a person has mostly negatives, then they should clearly have a negative score.
- If a person has only positives, then they should clearly have a non-negative score.
- If someone who previously had lots of positives gets a negative, this is interpreted by the system as "This person could very well be a con man! I can't be sure, though, since it's just one rating. Better show ??? just in case".
- If they then get several more negatives after the first negative, the ??? will turn into a negative score, as it should.
- If they get positives after the first negative, then this is interpreted as "Oh, it looks like that negative is probably wrong. I guess I can now mostly ignore it."
See the full algorithm here: https://bitcointalksearch.org/topic/minor-trust-score-algorithm-change-1066857
It's entirely legitimate to give someone a new positive rating just to negate a negative rating. (In this case you should explicitly respond to the negative rating you're negating.) It is not legitimate to keep deleting and reposting negative ratings to put the system back into "this guy just turned scammer!" mode. People who do that shouldn't be trusted.