The one and only time I went to a quickie oil change place, when the kid handed me the bill, it included a charge for an additional quart of oil. When I inquired, he informed me that my vehicle, a full size '92 van with a 5.7 TBI engine, needed six quarts of oil, and the standard rate included only five.
When I told him that I had change it myself many times, and it takes five, he pulled the dipstick, and sure enough, it was overfilled. He removed the extra quart, and showed me the computer screen that told him six quarts was required.
It's not always a barely-sentient worker messing up.