In over 30 yrs. of reloading, handgun, bottle neck, and shotgun, I have never experienced one single mis-fire. I'm not special, or other wise better at reloading than anyone else, I just make sure my primers are completely bottomed out in the pocket.
A properly seated primer will be below flush of the case head, but this does not mean that just because it is below flush, that it is completely seated, not at all. I prime on my press using a priming die, so it may feel slightly different than the feel of other type priming tools. But either way, when a primer is seated all the way, it will have a definite feel that it just won't go in any further. Resistance is one thing, but if it will seat deeper, then it it isn't fully seated yet, there needs to be some feeling of pre load against the anvil.
If a primer will detonate on the second or third attempt, it is about 99.9999% certain that the primer wasn't seated all the way, and especially so if it is doing this with reloads, and not with factory ammunition. The inertia of the firing pin drives the primer deeper, instead of inflicting a deep enough dent. If a primer can be moved by the FP inertia, it will often produce light looking strikes.
GS