You can learn a lot about whether or not a unit will stand up to the rigors of high-volume usage by attending a live demonstration and closely examining the unit's overall construction, especially the components that users interact with most frequently.
Are the components inside the paper drawers made primarily of metal or plastic? What about the document handler, does it seem sturdy or flimsy? Insist that the person doing the demonstration perform a print or copy job that takes at least five minutes. Did the machine run smoothly and quietly or did it shimmy and rattle? Also, keep in mind that even the most reliable machine will eventually need service. Insist on meeting the service manager and getting service references before you leave.