Never post a pair in their own box alone. It arrives crushed, and for an unworn pair the box was part of what the buyer paid for.
The method
Stuff the toe boxes. Paper, not newspaper against suede. Unsupported toe boxes crease permanently under any weight.
Shoe box inside a shipping box, with space around it. Two to three centimetres on every side, filled so nothing moves.
Tape every seam of the outer box.
Do not tape the shoe box itself. Removing tape takes the print with it, and the print is part of the value.
If there is no shoe box
Wrap each shoe separately so they do not rub against each other in transit — sole against sole marks uppers.
Materials
Suede and nubuck mark from almost anything. Bag them.
White midsoles pick up colour from printed paper. Use plain.
Weight and size
A sneaker box in a shipping box is bulky and light, which is exactly the shape couriers bill on volume rather than weight. Work your rates out from a real quote for a real box rather than from the weight on your scales. How rates work.
Photograph the packed parcel
Ten seconds, and it settles any argument about how it left you.
Questions people ask
Can I post without the original box?
Yes, if the listing said so. Wrap each shoe separately.
What if the buyer wants the box kept pristine?
Then the double-box method is not optional.
Who pays if the courier crushes it?
The claim is yours to make; the buyer is covered meanwhile. How that works.
More: packing an order.