Here is a new one: payroll checks that were cashed for employees of a business are being deposited to the personal account of the business owner instead of the business account. Would you file a SAR for un-registered MSB check cashing activity?

I don't buy the MSB thing. The business is not an MSB if it cashes its own payroll checks. It doesn't make sense that they would be deposited into the owner's account, though, but that probably has more to do with tax evasion than MSB activity.

So, if I disregard the MSB issue since I will assume that the business is the one cashing the checks for the employees, I cannot disregard the fact that they are being deposited to the owner's personal account instead of the business account, and want to file a SAR for activity that has no apparent legitimate purpose. Does anyone disagree?

I wholeheartedly agree with a SAR filing, if you believe what the customer is doing is suspicious or cannot be explained as a legitimate business transaction.

You don't have to believe the customer is doing something illegitimate or illegal to do a SAR. You only have to believe that what the customer is doing has no reasonable explanation or legitimate business purpose.