I have many user's who work on a sales floor and need to be able to open these files just to view them so that they can confirm that the artwork they are getting from a customer is correct before passing it on.

I do not want to purchase Adobe Creative Suite licenses for these users so that they can simply view these documents. What is the cheapest and best alternative to the Adobe Creative suite that will realistically open all (or at least some) of the files they are likely to receive?

Currently I have tried to use XnView with Ghostscript, Inkscape, and Adobe Acrobat Reader but even with all these combined we still can't open many of the files that we receive.