Don't explain things to sales people, just tell them what to order.
Dear sales people,
I told you we need a display port to vga adapter because only one came with the computer and the user has two monitors. I then went on to explain that the other two cables were useless because one was a display port to dvi-d (the user only has VGA monitors, can't convert dvi-d) and the other was a DMS-59 to dual DVI-i (the dvi looking connector that is for splitting into two, of which there was none on the computer and even if there had been no dvi-vga converter was present). However, this explanation was only an attempt to inform you of what went wrong so that it can be avoided in the future.
If I tell you that "we need X because Y was wrong" DO NOT ASK IF Y IS THE CORRECT THING TO ORDER!!