When and how to provide proof
If you are trading or gifting a character, simply say that you have traded or gifted them to X user. No proof needed. But keep in mind that the character will lose their resale value this way, if they are under level 5.
If the character is at or beyond level 5, whether you gift, trade or sell, it doesn't matter how you word your comment as long as you state the new owner's name. No proof needed. The character's resale value will be permanently marked as "unlimited".
If reselling an under level 5 character, you will need to state that you've sold them and provide proof together with the amount they sold for. The proof can be:
link to a comment chain where you clearly discuss the sale
screenshot of a discussion where you clearly discuss the sale
screenshot of the money transaction going through with any personal information censored (real name, address, email)
Proof can also be provided privately either by messaging @KatMasterlist or @KatAkillus on