OP, take a look at my trust history and you'll see that there are probably more negatives than positives.  Does that mean you can't trust me?  No (though I'm sure there are some members who'd tell you otherwise).  Most of the red trust I've gotten has been from members I'd previously tagged for various misdeeds like account selling or abusing bounties.  The same is true for many members on the default trust list, because a lot of them are or have been active scam busters and have thus gotten a lot of negative trust in return from members they've busted.