If you look at your card account online, (at least my AMEX and VISA work this way) you have two categories of transactions - pending and posted.
I've found that most gas stations will put an inflated amount into the pending category, and when the transaction moves into the posted category it will match the amount on my receipt. I check my online accounts on a daily basis.
The only time I've ever had a problem with gas charges was when Target got hacked and my card number was used to buy fuel from Denver to Houston. One simple call to AMEX got the fraudulent charges removed immediately.