To give a concrete example of what you're describing (one that no longer works) - this is from memory from an earlier discussion here on HN - years ago someone

To give a concrete example of what you're describing (one that no longer works) - this is from memory from an earlier discussion here on HN - years ago someone discovered that FedEx tracking numbers for Apple products were essentially serial in nature. In other words, if you ordered an iPhone and got tracking number X, and then a week later you ordered another one and got tracking number X + 500,000, it meant that Apple had sold 500,000 products online in that time period. Turns out that number was highly correlated with Apple earnings. The person in question claimed to have sold highly accurate "Apple earnings predictions" to hedge funds for 100K-200K per quarter per hedge fund.