Old tricks
 

I went to a Mobile gas station and magically put 12.8 gallons into my 11.9 gallon tank. I realize that there's the filler neck to consider, but theres also the fact that I actually drove to the gas station so my tank wasn't completely empty either.

Which gas station? I'll be in Buffalo next week and I don't want to go there.

Bad fuel pump at the station?

I think this may be more common than we think. I saw a post somewhere (I think anouther board) where peoples scangage readings of fuel used per tank was lower than the pump readout only at specific stations. Something to look out for guys.

it's had to tell with a single fill up, if this tank lasts a long time then you just over filled your tank in to the expansion space at the top that is there to give the gas space to go when your tank of 55F gas gets left in a parking lot on a 110F day.

One time I put 16 gallons into the 20 gallon tank on my van. I just wanted to top off before going downstate. I had never had problems with the fuel gauge and I had 3/4 tank left so I know they were screwing me. Had I really been closer to E and put 30 gallons into my 20 gallon tank, Id have a better case. That was also one of the stations that was fined for gouging after 911 and Katrina.

Theres also this one station downstate (Stanwood BP), that for whatever reason, makes my gauge read slower. 2 different occasions, about 6 months apart, 2 different cars. The only 2 times Ive gotten gas at that station in years (I try to avoid it because they make you pay first). And after filling up there, my gauge goes down like 3x slower than anywhere else. But next tank from somewhere else is perfectly fine, so its not like it gummed up the float. I drive the same highway back up north at the same speed and same time of day as I do any other time. And I end up getting the same mileage, when Ive used about 3/4 tank the gauge starts coming down faster and when I calculate the next tank it comes out the same. The car doesnt run any different.

you really want to find out go there with a container with known accurate readings test it out..

Read an article the other day of the shutoff valves in gas stations not counting off exactly when gas starts flowing...sometimes you pay more and sometimes you pay less. If that happens walk right into there and talk to there manager normaly they will refund you money so they dont have the big-wigs come mess with them....its a common problem ...look out for it.

That may not be the best way either because if the amount is small enough, a single gallon may not detect it unless you have some sort of graduated cylinder. I recently reported a gas station in my city for that same reason. My gas logs are pretty accurate so are my fill times and distance traveled, therefore when I see a 1 gallon discrepancy where their shouldn't be one, I smell problems.

However I still want to know how its done, the amount of money paid matches the read out of gallons, so how is scam potentially pulled off?

This was about 30 miles north of Buffalo, so you probably won't run into that one. It was a Mobile gas station though, in a place called Wrights Corners.. entirely my fault too, there was a Tops gas station right across the street for 5 cents cheaper, but I was too busy to wait in line, haha that'll teach me!