General Ledger by L. Joseph Shosty

The first in its series, a mercenary arrives on the lush planet Bergot to steal a priceless idol from a temple deep within the indigenous race's holy land. Accompanying him is an eccentric robot programmed to sell him useful items at a steep mark-up. What begins as a dangerous caper soon turns into an all-out fight for survival. Succeed, and they'll be rich. Fail, and they will incite an intergalactic incident.