Indeed. That is why civilized legal systems recognize contracts because contracts permit parties to allocate all manner of reasonable conventions among themselves.

Why OP chose to enter this particular contract with OS, if he wanted protection from both the weather and the duty to inspect his property on its return, is beyond me.

Certainly OS could insist on a careful structural inspection of any checked luggage and then another inspection upon return. That is what happens with extremely valuable shipments. But, it is impractical. Thus, OS (and other carriers) propose and passengers seem to accept, reasonable terms.