Electronics sell well live for one reason: a camera can prove the thing works, and no photograph can.
Sign out before you post
Do this before anything else, and do it properly.
A phone, tablet, laptop or watch that is still signed in to its previous owner's account can arrive unusable. The buyer cannot set it up, cannot factory reset their way past it, and has bought a locked object. It is the most common way an electronics sale turns into a return, and it is entirely preventable.
So: back up, sign out of every account, remove the device from your account, and then reset it. Do it in that order — resetting first can leave the device still attached to your account. Say in the listing that you have done it. Account security.
Wipe everything else too. Photos, messages, saved passwords, work accounts. A device you post is a device you no longer control.
Show it working
Boot it on camera. Let the screen come up. For a phone, show the settings page with the model and storage. For a laptop, show it running. For audio, play something.
Thirty seconds of a device actually working is the most persuasive thing in this category.
Say what comes with it
Charger, cable, adapter, case, box, stylus, remote. A buyer who has to spend money on a charger before using the thing has effectively paid more than they bid.
Condition of the battery
For anything portable, say what you know: how old it is, whether the device reports battery health, how long it lasts in normal use. "I do not know" is fine. A confident "battery is perfect" is not.
Untested is a real listing
If you cannot test something, say untested in the title, not in the small print, and price it as untested. Selling for parts is a normal and respected listing here. What you can and cannot sell.
Delivery
Batteries are the complication. Packing electronics covers it, and the short version is: ask your courier before you promise anything.
More: how to sell on Metzee, pricing electronics.
Questions people ask
Do I have to include the original box?
No, but say whether you are. For anything collected or recent, the box matters to resale.
Can I sell a device that is still on finance or instalments?
Not if you do not own it outright. That is somebody else's property until it is paid for.
Should I reset before or after signing out?
Sign out first, remove the device from your account, then reset. The other order can leave it locked.