I've never read a Retief story that I didn't enjoy. I read this one first back in 1968, again in 1977. Searched for it high and low and found it in a reprint back 1n 1996. Read it twice since then. I'm letting my copy go 'cause w/PBS I'll be able to find it again for another read perhaps in 2010(?)
SciFi - humor - Retief is a Diplomat with the Terran Corps, but his methods of action are more like James Bond than any diplomat. The planet Quoppina has just converted to a dictatorship for the benefit of one tribe. Looks like the work of the Groaci, a lizard like race always in competition with the Terrans. Retief is called in to investigate and the adventure is on - oh yeah the locals are made of metal, and roll on wheels - quite a change.