This is such a basic issue that I don't understand why USPS or some other shipper w/ bricks-n-mortar haven't stepped up to offer some sort of package shipping certification.
If I was the seller it could work as simply as me bringing the item to a shipper who would take their own photos and weigh the items being packaged up as well as some check that the item is as being described to the recipient. In turn the shipper would get an extra fee.
For high value items (i.e. like OP's camera) it would certainly be in everyone's best interest and platforms like ebay, Facebook, Amazon could insist that all parties use this type of service or relinquish their ability to dispute.
If I was the seller it could work as simply as me bringing the item to a shipper who would take their own photos and weigh the items being packaged up as well as some check that the item is as being described to the recipient. In turn the shipper would get an extra fee.
For high value items (i.e. like OP's camera) it would certainly be in everyone's best interest and platforms like ebay, Facebook, Amazon could insist that all parties use this type of service or relinquish their ability to dispute.
Too over simplified??