Pinned straw:
OBM basically uses an arbitrage business model to make money...
Something like this as I understand. Assume they have a client with a blog about mould issues who wants to monetise the blog.
The difference between what they paid for the traffic and what they get for the CPC is how they make money.
The bots are a bit of a dirty secret. OBM obviously don't want Google to think they are pushing through bot traffic, but OTOH, they are OK with as much of it as they can get away with. So the issue they had that "reset" the revenue of OBM was, almost surely, that too much bot traffic started getting through undetected by OBM. This slide from April shows where the bot problem sits.
Anyway, that's about as best as I understand it. Hopefully I'm not totally wrong!
@Summer12 from memory there was a SM meeting on the 30th August earlier this year. There is also a brief discussion on the company in the Baby Giants podcast dated 6th October if your interested.