When Josie Leavitt, co-owner of Flying Pig Children's Books in Charlotte, Vt., agreed to let two long-time shoppers who summer in Vermont, sisters Rose, 12, and Nora, 13, intern at her store over the summer, she had no idea what good salespeople they would turn out to be. "We did a barter," says Leavitt. "We kept track of their hours and paid them in books. They thought this was cool."

The girls' work was to take five books at a time and write short reviews that would fit on a 3"×5" index card. Leavitt has nothing but praise for their reviews and their effectiveness as a sales tool. "When a parent picks up a book and says, 'What is this about?' I hand them a card and say, 'This is what a 13-year-old thought about it,' " she says.

The cards sell teen shoppers, too, on books ranging from classics such as Harper Lee's To Kill a Mockingbird to contemporary novels such as Ann Brashares's The Sisterhood of the Traveling Pants and Louise Rennison's Angus, Thongs and Full-Frontal Snogging. "Kids talking to kids works better," says Leavitt, who loaded up the girls with a pile of books and index cards to take home at summer's end. "It's giving us a chance to sell things we might have forgotten about."