Most foreclosure auction attendees are house-flippers who fix up their buys then put them back on the market — the increased property value comes from renovations, not market shifts, and the profits are modest on a per-house basis. The real profits come from quantity, and not many investors have the stomach for that kind of grind. Consequently, the auctions draw a limited group of regulars. Naturally, the regulars turn from rivals to acquaintances over time.

Picture the scenario: Twice a week, every week, for three months, John, Mike, and Sally see each other at the auction. They all do their homework and each have a good eye for undervalued property. So twice a week, every week, for three months, John, Mike, and Harry target the same undervalued properties. One day they all bid on a $350,000 condo in SOMA. John holds out the longest, and he gets it for $475,000. Another day, a $625,000 two-story in Pacific Heights, and Sally gets it for $780,000. And so on. Eventually they realize it makes more sense to just team up, keep the prices down, and split the bigger profits on each of the properties. Why split the goods three ways at market price when you can split it three ways at foreclosure price?

When some new investor, Bill, comes along, John, Mike, and Sally approach him. They won’t necessarily tell Bill to not bid. They won’t necessarily invite Bill into the crew. Most likely, they’ll offer Bill some money to pass on a certain property. Bill is new, and he’s just been cornered by three veterans who are offering to pay him to do nothing. So Bill accepts. And now Bill is part of the conspiracy, and will be arrested along with the others, because the FBI cameras or agents were watching the whole time.