The problem with novices buying used is that we don't know what we're buying.
Yup, I avoided buying used for the same reason. I can't tell the difference between a bike that's only a tuneup away from being a great bike, and one that would require rebuilding everything. And I didn't have the faintest idea how to size a bike for myself.
Honestly, I was initially overwhelmed by how important everyone seemed to think it was to get the "right" bike to commute on. One inexpensive bike later, it seems to me that overly worrying about the type of bike matters only if you've been commuting for a long while and have distinct preferences on what you get to work on, if you're someone who commutes a long way to work (where speed might really be an issue), or if you're someone who is into mechanics and bicycles and enjoys the hunt for a perfect bicycle. For a novice going ~7-10 miles and just wants a servicable vehicle, I'd bet pretty much any new bike from a good bike shop (i.e., one that will talk to you) serves fine as a starter.
Cheers,
JOnobie