printing cmyk is like a shooting in the dark. your colors will also be affected based on what paper you use. etc.
pdfs don't always display shit correct. there can be white lines, etc.
you should show the client the pantone "chip(s)". if possible.
If they are only proofing copy, then tell them to ignore the colour in the file.
Job Done, move on and do the next shitty ad for them.