A Fuel’s Errand

I work at a petrol station. A woman walks into the shop (she didn’t drive) and holds out a little canister.

Customer: “Can you tell me what the oil-to-petrol ratio is in my lawnmower petrol?”

Me: “Not here. I’m behind the register, and I’m working alone.”

She holds the can forward and shakes it a little.

Customer: “Yes, but you can tell by smelling it, right?”