A bike that survives the auction still has to survive a courier. This is the part of buying at distance that buyers price at zero and that occasionally costs more than the discount they were chasing.
The rear derailleur and its hanger take the most damage, because they protrude furthest and sit at the corner of the box that gets dropped. A bent hanger is cheap and common. A derailleur driven into the spokes is neither.
After that, in rough order: disc rotors bent by pressure through the side of the box, lever hoods scuffed where they press against cardboard, and paint worn through at any point where a loose part was left resting against the frame for a few hundred miles of vibration. That last one is the reason good packers zip-tie everything.
Ask how the bike will be packed. The answer separates sellers quickly. A good answer mentions removing the rear derailleur from the hanger, fitting a spacer in the fork and a brace in the rear dropouts, deflating tyres partially, and padding the frame at every contact point. A vague answer usually means the bike is going in the box the way it came off the stand.
If the seller offers shop packing, it is generally worth the surcharge. It is the cheapest insurance in the transaction, and a shop that packs bikes weekly makes fewer mistakes than someone doing their first.
Photograph the box before you open it, from several sides, including any crushing or punctures. Then photograph each layer as you unpack rather than after. Both carrier claims and marketplace buyer protection turn on evidence created before the bike was assembled, and once the box is flattened and the bike is built, distinguishing transit damage from pre-existing damage becomes close to impossible.
Check the hanger alignment before the first ride even if nothing looks wrong. A hanger bent a few degrees shifts badly and is often mistaken for a drivetrain that needs replacing.
Local pickup removes transit risk and lets you see the bike, which is genuinely valuable on a used carbon frame. The cost is a much smaller pool and often stiffer competition for it. Shipping opens the whole market, and the right way to use it is to treat packing quality as part of the bid: a well-packed bike from a careful seller is worth meaningfully more than the same bike from someone who has never boxed one.
Sizing a bike you cannot test rideandspotting carbon damage in listing photos cover the two checks worth making before the shipping question comes up. Current complete bikes are on the Shimano 105 board.