Around here they will dip any tank, not just commercial.
Dealerships have been fined heavily just for having used vehicles on the lot that a previous owner has used red diesel in.
So some dealers will dip a tank upon trade in and if it comes up red, they will not take the trade.
And it takes very little to test positive. My mechanic friend says he has a customer that had run several tanks of normal fuel through the engine after using just a small amount of red but still came up positive and was fined.
A dealer will also void the engine warranty if they find red.
All in all it just isn't worth it.