I've been reading that some of the touchscreens on haphazardly built tablet-style voting machines had trouble registering votes. Like the guy, whose video is going viral, who kept pressing the Obama option, but it kept highlighting Romney; and when he highlighted Jill Stein, it was fine. So the picture is being painted of the "biased machine."
Both mail-in and in-person have their drawbacks, but I think Mail-In= more votes because it casts a wider net of responders. Will there be skewed and perhaps fraudulent votes? Absolutely. What is statistics without outliers, variations, and deviations?