i had my winters taken off and all-season installed at Wal-mart.
you might be saying "whaaaat?"
but they did good job. I was there to observe, and they made good use of the torque wrench after torquing each wheel.
and it's only $5 per wheel. (my rims and tires are already well-balanced individually)
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However, I used to be guilty of over-torquing, when I worked at my parents' shop. Never enough to shatter anything, though. I was very good to customers' cars. all wheels balanced to perfection(given the old balancing machine), never had ANYONE complain on my work.
I cared like I would when I worked on my own car, and that took extra 2-3 minutes per car. .... but you just don't see that in many shops. (never even close at honda dealer where i bought my Fit, new)
sucks. hope your issue gets resolved satisfactorily.