We certainly can't help based on YOUR screenshots since you don't see any issues.
Where is the client's screenshot. They must be using Acrobat or Reader to view it. All bets are off otherwise.
Sorry, I see the client's shot in there.
My guess is they're using a non-Acrobat PDF reader such as Mac Preview.
The top shot is what the client sent back to me - the top image looks wider on each side then the one below it. The two underneath are closeups of the InDesign and the PDF respectively. They look fine. I've been told since that they are using Akrobat Reader to view it.
In Reader, have them try View > Show/hide > Toolbar items > Show page display tools > Line weights. Does that help?