I had a one-day rental from Avis in downtown Victoria BC last summer; drove ~70 miles (topped off ~20km / 12 mi away), and pulled into the garage with the needle touching the edge of the F mark; email receipt showed up 15 min later with a $35 refueling charge ... when I went into the office the next morning (receipt in hand, showing time and place of purchase) and asked the manager about it, his reply was "you have to fill up within 10 km / 6 mi"
"uh, please show me where in the contract it says that"
"that's just our policy sir"
he offered to knock it down to $15 and I wasn't in the mood to argue any farther as we had a floatplane to catch