Checking vague fees, tip prompts, and tiny print can keep a restaurant bill from quietly charging diners twice before you spot it.

You’ve walked down the grocery aisle and spotted the big numbers: “50% off!” “BOGO Half Price!” “25% Extra Free!”.

Which meant that most days of the week, I was staring down two to four toddlers armed with nothing but my charm, some creativity, and a room full of toys and books that they were already bored of by 9 ...