My bud runs a used car dealership. You will be amazed at how much paperwork he signs as the bank just to deposit cash from the same car buyers who paid mostly paid cash for cars.
I had a client, a 19 year old female college student who was audited by the IRS as she took out a Bank loan for $8,000 that her father co-signed, cashed the check at the bank and then used the cash to purchase a used car at a dealer.
I convinced the agent to drop the audit by providing a few documents. It was triggered by the auto dealership cash deposit.