I've always been in the camp that you get what you pay for.

I wouldn't ever have anything done at a shop that allows customers to buy their own parts . A portion of the profit of a shop is the margin of profit of the part cost from wholesale to retail, generally 30-40%.

My reasoning is that if a shop is not making full profit on a job they could be inclined to reduce labor time to help make up the difference. That could mean they would be cutting corners and/or not be as careful or interested in doing the job correctly.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas