Answers
It's a matter of banking compliance and KYC. There is no specific procedure for transferring money. It depends on each bank.
Regarding your question, please be informed that due to recent legal amendments to Greek Immigration Law acceptable ways of the property acquisition amount are the following: The investment amount to be covered by relatives of the investor up to the second degree, upon the respective relationship proof certificate; payments through credit cards are also acceptable.
Regarding the transfer of funds, you will need to open a bank account in Greece and receive also a Fiscal number from which payment will take place to the seller.
By the end of your efforts with a view to a Greek golden visa, you will need advice from a migration agent.