Check the rear dropout alignment. The tools to do so look like T-handles with adjustable cups on the ends. It's a 5 minute job.
Better yet, have that same mechanic at the same LBS do it for you:
If it turns out they are not parallel - or close to parallel as they should be, yell back at him:
"You've been servicing my bike for 8 years? What am I paying you for?"
A "payback is a *****" opportunity awaits...
Wheels installed in quality BUT misaligned dropouts are going to end up with bent axles - and accelerate the eventual - a snapped axle.
=8-)
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5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life