> As it often happens, undoing the mistakes, oversights, or just
  > plain poor workmanship gets costly in a hurry, and I'm asked to
  > write up a report (complete with photographic evidence) of what I
  > have found.
  >
  > Here's my question: Before sending my report to the customer, do I
  > have any obligation to attempt to contact the technician and tell
  > him what I found?

Unless you're somehow obliged to protect and defend a fellow member of
the Worshipful Order of Player Piano Repairmen, I don't see why it's
your responsibility.  The initial contract was between the technician
and the customer, so you are not a party to any negotiations.  Perhaps
the customer himself might want to arrange for the errant technician to
see your report and address the points you have made.  The technician
would then be free to disagree with your conclusions or to make changes.

I'm assuming that your reports are worded in a professional manner --
i.e., that you refrain from referring to the technician as "a lumpish
dolt from a limited gene pool," even if true.  Instead, you might say,
"The pneumatic bellows appears to have been rebuilt with silicone
bathtub caulk, reinforced by surgical gauze.  While the energy and
resourcefulness of the rebuilder cannot be denied, we have found that
these materials typically exhibit long-term durability problems."

In other words, you always say something nice before issuing your
condemnation.  This is the technique typically used in the criticism of
academic research submitted to scholarly journals, as we learned in
graduate school.

M. Kinsler