I look after a fleet of taxi's & they are the worst for low fuel levels.

I took to checking fuel levels years ago and stating that I would add a tenners worth of fuel, that would be added to the bill.
A few grumbles were forthcoming, but overcame swifty when explained they either go put some fuel in, or I do.

It's a habit I've got into now & 'normal' customers seem happy once I explain to them how much fuel is in a late Passat / Mondeo fuel filter, along with the fact that some EDC systems do run rough with low fuel levels.