Proof of ownership is not done by sending satoshis, its done by signing a message.
Anyway, nobody believes, that there exist any coins.
Its not the first offer of crazy amounts here.
Sagara offered 7500BTC for sale.
OK, so sign at least a message with an address containing even "only" 50BTC.
I bet 1:10, this will never ever happen...

Just to remind, min 50BTC=425000USD.
Even the real,big, existing and serious OTC-Desks, offer lower minimum amounts.