Another reason why a neutral rating may want to be used is if you are on default trust, but do not want to leave outright negative trust, for example if someone is requesting a scammy loan however appears to be doing so because they do not know any better. The neutral trust could be used as a "warning" to be used and if similar behavior is used in the future then an outright negative trust may be warranted
That's one good reason, but usually the red warning was also there for a good reason because of the high potential and likelihood of a scam being committed and served as a good warning but now that warning won't show up. I like the idea of neutral trust and is good if you want to leave a positive comment without issuing trust but I don't think it's going to work very well for several reasons. Dishonest or angry people aren't suddenly going to start leaving neutral trust instead of negative to be 'fairer'. Also, if I or anyone else leaves a neutral feedback on someone voicing their suspicions of a user's behaviour or the high likelihood of them scamming they'll still likely retaliate with negative feedback.