That's setting the bar pretty high. There's always going to be some level of personal preference as regards things like comma positioning and whether or not to split a sentence, or where, so there's not an objective measure of perfection. If you're just listening and reading, as opposed to listening, typing and reading, you can devote more attention to error checking. I find I'm more attentive to errors when I'm checking someone else's work; people sometimes get tunnel vision about their own work, and I'm as guilty of this as anyone. Mike@CW has told me about experienced transcribers who have been surprised when they've looked at their work with the eyes of an editor. But that's part of the reason for the edit process, and the approval process offers a third pair of eyes.