The biggest clue is the frequency and volume of checks. Imagine being at the bank and your customer who ordinarily deposits a million per month is now depositing 6 million per day.
I'm certainly not arguing that the banks are innocent victims in this. It's interesting to see your take on the article (presuming, from your screen name, that you're looking at it from a CPA's perspective). Personally, my interest is in the manner in which real estate fraud is committed (and, hopefully, can be prevented).