Search - Witch's Business

This is one of Diana Wynne Jones' earlier books. (It was originally published in 1973, under the title 'Wilkins' Tooth')
It's definitely aimed at a younger audience than many of her books - it's a kids' book, probably for people around 10. But I didn't feel that it had the 'condescending' feeling that I complained of in 'Dogsbody' at all. I admit that I enjoyed it!
In it, a group of kids decide to make some pocket money by going into the revenge business. Soon this leads them to tangle with the tough gang from the neighborhood, the two 'weird' sisters that no one likes, and some other kids from the neighborhood. Everyone wants revenge on someone, and the situation is getting complicated - but it goes from complicated to worse when the strange old Biddy who lives in a hut and is suspected of being a witch begins to warn them off... revenge might be "Witch's Business" and kids have no right to cut in....