Two sentences prevent most returns in this category, and most listings contain neither.
"Working" without switching it on
If you have not powered it on, the word is untested, in the title, at untested prices. That is a normal, respected listing. The other version is a return.
Not stating the region
A disc or cartridge a buyer's console will not read is useless to them. The marking is on the spine. Show it.
Saying "complete" loosely
Complete means everything that was in the box when it was new. If you are unsure, list what you have instead of claiming the word. Describing games.
Not taping the case shut
The hub lets go, the disc comes loose, and it spends the journey against its own case. One piece of tape.
Ignoring the save battery
Older cartridges keep saves on a battery with a life. Say whether it saves, or say you did not test it.
Treating a seal as proof
It is a description, not a certificate. Say where it came from and how long you have had it; buyers who care about sealed items know the difference and trust the seller who says it first.
Pricing loose against complete
Three states, three markets. What games are worth.
The one that costs most
Selling a console without saying what is missing. Every absent cable, controller or power supply is money the buyer must spend before it works, and they will count it.
Questions people ask
Should I clean a disc?
A light clean from the centre outwards, and never to disguise a scratch.
Does a replacement case matter?
Only if undeclared. Say "replacement case".
Are loose cartridges worth selling?
Yes, in platform lots.
More: selling games, packing them.