My parents meticulously check every penny of every purchase on the receipt. The compare the receipts against the credit card statement. They check utility bills, etc. And they are frequently finding mistakes.
I rarely check receipts and bills closely. I understand that I’m probably being slightly overcharged on a fairly regular basis, but I have decided that the time and energy it takes to carefully audit every single receipt and bill is not worth the money it might save me. On the other hand, I do attempt to at least make a quick estimate of the correct amount of the receipt or bill. It takes only a few seconds to decide whether or not the total is at least in the ball park. I usually spend about 30 seconds scanning down my credit card statement to make sure there is nothing suspicious on there. Twice I’ve discovered that I was double charged. The first time, I disputed the charge with the bank and was eventually credited that amount. The second time, I called the company and they credited the amount back to my card. A few seconds of work can save you money.