I well I seen Diesel fuel accidentally put in fuel tanks along with Kerosene. I even gotten gasoline that had lots of water. It is frustrating to have this to happen. Here our unleaded gasoline is dyed yellow and the diesel has no dye but is oil color as Kerosene. We can even get bad fuel that will not even light by match or torch.

I once gotten Kerosene as the delivery driver had put it in a diesel tank. My tractor sounded like it was going to blow up. I got over a quart of water in 5 gallon gasoline once. That one cause me headaches as the 300 lb plus tiller died in the middle of a deeply tilled garden patch. One customer filled his zero turn with 5 gallons of diesel by mistake.

So yes things happen by accident and may or may not be the operator/owner causing it. Just chalk it as it happen and move on.

Right I got in an UTV that has a brand new plug in it the is bad. I know the customer is going to say he replaced the plug. Doesn't matter it is bad.