I think the scale of operation has an impact, too. The first time I tried to hatch shipped eggs, they came from a rather large online dealer of hatching eggs. Of the few eggs that did hatch (just 6 out of 2 dozen), one had been mislabeled and was obviously not what I had ordered. No wheaten bird starts out with black down! The next time I tried, I ordered from someone who only raised one breed of chicken. I got 14 eggs, 13 developed, and 11 hatched. Perhaps the folks who are a one or two person operation can better keep tabs on the health of the breeding flock, the freshness of the eggs, and the packaging.
Like someone else mentioned, try hatching some locally obtained eggs. Better yet, try hatching some of your own. If you haven't paid $3-$4 per egg, you may feel you don't have as much at stake and the temptation to "help" during the hatch won't be as intense. A lot of the helping does more harm than good anyway as it allows weaker chicks to enter your flock.
Like someone else mentioned, try hatching some locally obtained eggs. Better yet, try hatching some of your own. If you haven't paid $3-$4 per egg, you may feel you don't have as much at stake and the temptation to "help" during the hatch won't be as intense. A lot of the helping does more harm than good anyway as it allows weaker chicks to enter your flock.