Pictures of the cards with your forum name and date on. Or your’re just another scammer trying it on with your “verified twitter”
since when proof of ownership clear the intentions of scamming ?
Since never, but at least, it proves that the seller has the items in hand so is a good step in the right direction.
Offcourse, escrow is mandatory, but why waste time with a seller that can't even prove that he owns the items that he is trying to sell?