Bismarck.Josiahfk said:
»you send a mule to his server with gil, give seller the gil and delete char. he sends the item to a new mule you make there and that mule can instantly move to your server with the item
Can't you make a mule on your server, make a mule on the seller's server...
Give the mule on your server the gil and hop it to the seller's server, at that point buy said item, give said item to the mule originally made on the seller's server then hop the mule back to your server.
Just safer, don't have to trust people you don't really know (or may not even speak the same language as you) with gil and hope they send something to you.
but yes, you'll need to have had the content ID (not the character itself I don't think) active for at least three months before you can transfer a character.