Another one of those nagging memories from high school... I read it as a paperback in the 1990s or so. It's part of a larger cycle or series of book, which I remember only because one of the three humans protagonists (2 men, 1 woman) is an overweight merchant prince of some sort that had appeared in another story I half-remember. The three are on a trade mission to a planet who's pre-industrial aliens look like winged bears when their shuttle gets destroyed, and their means of communications confiscated. For some reason they can't eat any of the food on the planet since it's toxic to them, so they have to ally with a faction of the aliens that friendly to them to try and overthrow the flying bear government before they starve - and they do so by teaching the aliens and giving them rudimentary tech, like machine guns that shoot darts.
This whole thing probably sounds like a rambling dream, but I know for sure this book exists, even though google seems to have no idea what I'm on about. Anyone here has any clue?