Several reasons for the shop to have used tires with about 100 miles. Some car dealers offer rim and tire upgrades. The shops they work with will offer a deal if they get to keep the factory rims and tires. Same way a customer might want their new factory tires replaced with a preferred brand. The shop may have also had a situation where they took back tires for whatever reason.
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When you get in debt you become a slave. - Andrew Jackson