I've gotten pretty good at eyeballing a straight arrow, but then I've had years of practice. I'll use an arrow straightener for really difficult shafts though, the kind with the lever and dial indicator.

When I make arrows, I straighten them repeatedly. I straighten them when I first get them. Let them rest a day or two so they can adjust to the ambient humidity here inmy area,then straighten them again. Then straighten them again before I cut the tapers. Straighten them again before I apply stain. Straighten them again before I apply finish. Straighten them again before I fletch. Only the worst will really need straightening again by that point.

I wind up with arrows that stay straight, as long as they stay sealed against humidity.