Firearms, ammunition and anything that fires a projectile: no. Not deactivated, not antique, not airguns, not parts.
Everything else depends on what the object actually is, and the honest answer has three parts.
What is clearly fine
Ordinary tools and kitchen knives. A chef's knife, a carving set, a pocket knife of the kind sold in any hardware shop. These sit in Home & Garden, Outdoors & Hunting or Collectibles and are unremarkable.
Militaria that is not a weapon. Medals, badges, uniforms, helmets, documents, photographs. A large and legitimate collecting field.
Replica swords and display pieces, where the thing is decorative and is described as what it is.
What is not
- Firearms of any kind, their parts, ammunition, and anything that looks like one closely enough to be mistaken for it
- Knives of a kind restricted where you or the buyer are — the law is about the type of blade, not the price
- Anything concealed as something else
- Anything you would need a licence to hold and do not hold
The part that is yours, not Metzee's
The licence question. If a licence is needed to sell or own something, you need it — being on a marketplace changes nothing. Metzee does not check and cannot hold one for you. Do I need a licence?
And the restrictions can depend on where the buyer is, not only where you are. A sale that is fine at your end and illegal at theirs is still a problem, and it is one you will discover when the parcel is stopped. What if a parcel is held or seized?
Couriers refuse more than the law does
Worth knowing separately: a courier can decline a parcel it is perfectly legal to send, and bladed items are a common refusal. Check before you list rather than after you sell. How to pack an order
How to list the ones that are allowed
Describe the object plainly, including the blade length and the material. Do not glamorise it — a listing written as though the thing is for fighting reads as exactly the listing that should come down.
Say it is a replica if it is, in the title. Not for Metzee's benefit but because a buyer expecting steel and receiving aluminium opens a case you lose.
More: prohibited items explained, do I need a licence, what you can and cannot sell.