Juvenile fantasy about a boy that is declared prince and must confront a dragon

[Jenn]

Published late 70's-90's.
I have a patron requesting a book she did not read but heard the details of about 40 years ago. It's a juvenile fantasy (possibly YA) about a boy that went out to seek his fortune and wound up in a kingdom where the population declared he was the prince they were waiting for. He was told that in order to be crowned, he needed to slay a dragon that was terrorizing the town. The boy spoke to the dragon in hopes of negotiating with him. The dragon said he just loved burning things. They worked out a deal that once a week the dragon would burn the trash at the town dump and leave the town itself around