Guess I didn't really say, I almost never candle and pitch. Just let them go. But before I put them in, I inspect closely for cracks or bad looking.
This is what I do too. If it's not near perfect, it doesn't go in. But I've only hatched my own eggs, I've never experience purchasing eggs for $25-50 a dozen or more/less and then question if I should incubate or not. That might be a total different story on what I would put in my incubator.
I have never candled an egg from my incubator, when the humidity drops I add water and give it a sniff test to make sure it doesn't have any bad smells. I've never had one bad so I'm not too sure what one smells like. I'm sure it will happen one day.. and that won't be good. I have such a sensitive sniffer that I can't eat eggs for 1-2 weeks after hatch.. that mix of egg and hatch smell makes my stomach turn. Oh no, I'm getting queezy.. blahhh