Just a little tidbit, from an Autocad user of 9 years....
Not everyone sets up their drawing the same way....
Your lines were probably thick because they setup their lines to be a given thickness, rather than having a color setup to be the thickness they need, and keeping the lines at a thickness of 0 (Glad Archicad has a Thin Line setting
)
Best thing you can do is have then print out their layer manager/and or plot format file. If you do your work with the same people each time, and they (hopefully) use the same layering system, you can set up a template that will convert everything to your specs.