From the FAQ (I'm assuming never traded means with each other):
Users that have never traded can’t leave feedback, however, if they mark each other as trusted or not trusted they are able to leave trustworthy, neutral or block feedback.
I'm not an LBC user but I'm not sure how would that be possible according to the statement above?
There is a confliction between LBC's FAQs and support reply I guess.
When I got the negative rating I had contacted LBC to help remove the negative rating which is not based on trading, instead, it happened due to disagreement.
They replied,
The feedback you received will not be removed. LocalBitcoins does not remove or edit feedback, unless it contains abusive, racist language, threats or exposes personal information.
My account rating dropped from 100% to 93% and I had to stop trading there because I felt that other traders will think of me as untrustworthy when they see my profile. That's the thing I don't wanted and so I quit trading.