PM me for reason.
Let me guess: taxes? Claiming capital gains while in reality you got the coins in other ways?
As attractive as this offer sounds, I wouldn't dare risk money laundering charges because of this.Basically just need coins from an aged transaction and the ability to sign a message from that old address.
The problem with that is that the "seller" can also still sign the same message, and if he too uses it for taxes, it might come back to haunt you later.
For that use case you have to exchange the whole amount of the address / or get the private key. Still possible.