In this case i will provide full info.. how i own the account to the auction winner..
I will answer evwry questions to prove that i own the account
even you can provide all the proofs that you got the account from an auction BUT you cant provide a signed message for the possible buyer to prove that the account is bought you can still claim the account back by saying it is hacked from you, there will be no guarantee for the possible buyer that you wont claim back the account tho so s signed message is a MUST in accounts selling unless the buyer doesnt know that