Myth-gotten gains - Robert Asprin

Aahz discovers that the shabby-looking sword he bought at a flea market in a remote dimension is Ersatz, leader of the Golden Hoard, a fabled collection of powerful magical treasures that can turn any ordinary being into a hero. They go in search of the other members of the Hoard, only to find that they're not the only ones looking. A dancer named Calypsa, working with Aahz's old friend Tananda, is seeking to collect them to free her grandfather from the dreaded wizard Barrik. Trouble is, everyone wants the treasures for themselves, and there are good reasons why the Golden Hoard is never all in the same dimension at one time.