I have three GDI Turbocharged vehicles. And with the Ktuner V2 (for reading ecu parameters through OBDII) I can make out roughly how good/bad the petrol is.
I'll give you a recent example. I got Vpower from Shell Battle Axe (Shami Road, Lahore Cantt). The knock control value the ecu had calculated was at 0.49 (around 95 RON) on previous fuel from the same station. After the new fill up, the knock control value shot up to 0.75 (80-85 RON) within seconds of driving.
So what conclusions can we draw from this? Fuel quality isn't even consistent on the same fuel station. It varies by a large amount from batch to batch. Unfortunately I don't have the time or the willingness to pursue the consumer courts.