The state of what arrives says a lot about how the person on the other end operates, and it is worth two minutes of attention before anything else happens.
Unremarkable from the outside. Correct postage, a plausible sender, nothing that invites a second look. The contents secured so that they do not shift or make noise, and sealed so that tampering would be visible rather than invisible.
Open it and compare against the listing before confirming receipt, not afterwards. Once confirmed, the payment has moved and the dispute route has closed, and discovering a discrepancy at that point leaves nothing to do about it.
If something is wrong, record it before handling it further. A photograph taken at the moment of opening is far more useful in a dispute than a description written a day later, and arbitration weighs what can be shown over what is asserted.
It is one of the few things a buyer can assess objectively and one of the most useful things to tell the next person. A note saying a parcel arrived secure and unremarkable is more informative than a rating, and a note describing careless packaging is a genuine warning.
Care with packaging tends to correlate with care elsewhere: accurate listings, honest handling times, sane dispute behaviour. It is not proof of anything, and as a rough signal it is more reliable than a star average.
Almost everything else about a seller is claims: their listing, their handling estimate, their explanation when something goes wrong. The parcel is physical evidence of how they actually work, and it arrives whether or not the order went smoothly.
The outer packaging carries the address you sent and the route it travelled. It does not need to survive in a bin where it can be read later. This is a small habit that costs nothing and closes the one loose end an otherwise clean order leaves behind.