John Goecke of FXWB Reprographics shared a tip when printing DWF files on the Océ 9800 or Océ TDS800. FXWB found that when architects and engineers used 0 weight pens in their AutoCAD drawings, the published DWF files would print out too light on the 9800 and TDS800 devices (especially on hatches and fills). FXWB found that using "Poster Mode" on these files ALWAYS resolved the issue. A 0 weight pen uses the thinnest possible line setting - one pixel wide. This varies from device to device. More times than not, the design firm would have an inkjet that would have an appropriate dot gain when used, making the fills buff, but when FXWB printed on the Océ devices (and they tested the Xerox machines also), the fills would be very hard to see.
Thanks for the tip John!