There were several knowns that we found with Prosper that Prosper never would put in their portfolio plans that gummed up the works.
It all had to do with second loans.
ORG'ers found that if a Prosper borrower took out new listings while there was still a loan in progress, no matter the duration, the likelihood of default on both loans approached 100%.
On the flip-side, any Prosper borrower that paid off more than 2 loans had an inverse liklihood, but ONLY if the amounts borrowed were near each other. i.e. one loan for $4,000 and the next one for $5,000, the next one $3,000, etc. Borrowers who go from one small loan and pay it off then start listings for one giant one were guaranteed to default.
A few Prosper borrowers had churned through as many as 6 paid-off loans.
So in Prosper's infinite wisdom, there was NO way to filter out second loans when Prosper started allowing them. If you had a PP and set to autofire, you could be picking up people who were very sure to default, but had a good credit score (for now). The listing on its own seemed OK, but then if you manually looked at the borrower's profile you'd notice the other loan out there barely a year old if that, and the new listing asking for substantially more money.
Second loans are another reason why going off the Prosper rating is stupid. Prosper never takes anything that we learned on .ORG and applied it back to their screening because that's not in Prosper's best interests to tell you exactly what risks you're facing or exactly what's happened in the past.
We like to sugarcoat the past and put up pictures of happy borrowers with perfect teeth.
Oh yeah, also the number of times a borrower has re-listed was also a BIG clue on the likelihood to default. Lots of re-listings == borrower is desperate.