When the cashier gave her a strange look, she had smiled and said as innocently as possible, "I'm buying books for my mum!" To illustrate the point she had waved her parchment (one-handed), on which she had indeed written a list of subjects she wanted to get books on, as illegibly as possible. The wizard had shrugged and moved on; Hermione's gold was just as shiny as anyone else's, and she hadn't bought anything illegal.