Buying a car used to be an experience so soul-scorching, so confidence-splattering, so existentially rattling that an entire car company was based on the promise that you wouldn't have to come in contact with it. In the past, a car buyer entered a dealership (a place that, free coffee aside, was plenty soul-scorching in its own right) much the way a fish entered a barrel guarded by an armed militia: Jaw gaping, eyes glassy and rolling, tender parts utterly exposed. By the time you were...