I suspect they would be difficult to train, because of their attitude. We see this with many wild animals. Dogs train easily, but coyotes and wolves, who are even smarter, are much more difficult to train.
One of my favorite nature vignettes, is a part of Planet Earth, by the BBC, about Cape Hunting Dogs[0]. It looks like a military assault. They are really clever, and work well, as a team.
But if you could train crows, they would probably be marvelous.