It is surprising that I can't see any Trados tags with the source text in the clean file but he sees them. The "Hidden text" is checked in the View tab, so if there is any hidden text, I should be able to see it.
So when you look at the file in Word, you see the paragraph marks at the end of the paragraphs, and the little dots for the spaces? If you don,t, go to Tools > Options > "View" tab > mark the "All" checkbox in the "Formatting marks" group. Click OK in the dialog box. Also check that the paragraph-mark icon in your toolbar is clicked on. You should now see little dots in the spaces and other marks.
If with all marks and hidden text visible you cannot see Trados marks or the source text, it is impossible that the customer can see them. Is it possible that you simply sent the customer the wrong file (the uncleaned one)?