Would like to share my recent experience in this regard -
I always prefer to fill up my Avenger 220 filling up the tank to the brim and then end up running it till its almost dry (i.e. 80-85 kms after it gets into reserve). Now I reached this Indian Oil pump in Goregaon E, Mumbai. There was a bike ahead of me in the queue. Now on my turn, I pushed the bike as I had switched it off, but meanwhile instructed the attendant that I needed 'tank full'.
At this point of time, the attendant pointed to the bike (which was taken out after a month, so was quite dirty) and started giving me advice that I should keep my bike clean especially the parts near the tank. Now after filling it upto the brim, I found that the meter showed more than 14 ltrs. I was quite sure that tank capacity of Avenger is either 14 or less. And also, realized that the guy didnt showed me zero.
With a straight face, i asked ki 'meter main pehle se kitna tha?' (how much was the reading before starting filling? Before, he could answer, I started shouting that how the hell he can fill 14 litres in a tank which has capacity of 13 litres with already 4-5 litres in it. I asked them to make a bill, mention the vehicle number and the model, and also asked them for the complaint book. Further, took out my cell and threatened the attendant directly, that I am calling the nearby police station and would certainly not let this go.
In the end, he agreed to take Rs. 300 less than what was on the meter of the pump!
My advice -
1. Be careful and attentive while filling fuel
2. If something smells fishy, be assertive even if you aren't that confident.