They keep the equipment pretty well so I doubt it was them that scratched the car Probably something kicked up off the road.
Are you sure it was the car wash?
How do you know it was from the car wash? I've never had that happen to me despite having my cars washed at various car washes in different cities. Sometimes, we only notice things, despite them been there for a while, and attribute it to the proceeding event. If it did occur at the car wash, you might want to ensure that the angle at which you are entering the is better aligned with the groove. This will help prevent your car from moving too much as it enters the groove. IMHO.
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