In general, I will return a knife that is messed up in a way that impedes performances, looks bad, or that I can't reliably fix myself.
Some recent examples include a QSP Leopard with the weakest detent I've ever encountered, a severely rusted Stedemon, and a special-edition Artisan Arroyo that was supposed to have pretty scales. The latter was supposed to look like the picture below. The scales are effectively suspensions in acrylic. The one I got for my wife just didn't have anything going on... It was almost entirely white and you could see through to the milling under normal lighting.