I do not have a Facebook profile, so the potential employers that run an "internet background check" will not trust me much.
Does that mean that I am not trustworthy? What I am getting at is that there are multiple levels of real and artificial trust. Being socially engaged on Facebook shows just that: you are are socially engaged and have lots of friends: you are probably a real person. Scammers can be very sociable people too, yet only their closest friends can hope to trust them, for the rest it's a facade: keeping up appearances. Buying followers to increase their Klout score.
Let's say this gets big. Do you expect attacks on your system and algo's to inflate the trust ranking? Would people leave fake reviews for themselves? Would people link up fake or stolen craigslist profiles?
If you happen to get the snowball rolling and the demand gets very high, do you think companies will form to cater to that demand? Scammers could create profiles that score well, and sell them priced according to their Trust Score. A luxury problem to have, but what is your view on this?
Finally how do you deal with people sending you e-mail or letters complaining their score is too low, or that your algo's are unfair, or that they didn't create that public profile, or want to remove a negative review? There seems quite a lot of (legal) hassle involved in the user problems that arise with such an application.