That's what I was worried about. Here's what I'm looking at used-wise. Am I crazy, or does this look like a decent used lens?
I'd stay far away from used ones. The lens is well known for being easy to knock out of alignment, even by those who are pretty careful. Most users do not have the equipment or the knowledge of what to look for.
If you must buy a used one, get it from Lens Rentals. They test them for sharpness and issues before selling them, so you are going to get a good one as long as there is no damage in shipping.
They seem to be out for now, but you might email Roger and ask.