A missing cover sounds like it would be visible without opening the product packaging (which would be the cover itself, no?), i.e. they can easily notice the om

A missing cover sounds like it would be visible without opening the product packaging (which would be the cover itself, no?), i.e. they can easily notice the omission by comparing the returned item against a reference image. In the OP case the product packaging was filled with dirt, which is not as easily discoverable without opening product packaging.