Positivs can be left for something as simple as "This user seems smart"
Merely being smart doesn't make someone unlikely to scam so that's probably not a good reason for a positive rating.
Although the evidence isn't that strong (as tends to be with psychology), the above statement is wrong. Not being smart makes you more likely of committing a crime (i.e. scamming).
Here. Also as per
Ellis, Beaver & Wright 2009, several personality traits correlate strongly with likelihood of committing a crime (scamming). However, in general I agree with you due to my conservative stance on issuing positive ratings as false credibility poses a huge risk of an user scamming somebody.