Charter a boat at Greece
The Greek Law as is today requires two people to have sailing knowledge certification. From Greeks it requires two sailing diplomas from a sailing school. From foreign residents if they dont have certification since some countries dont require them and there are a lot of self tought boat owners they should fill a declaration with the port police that says that they have the knowledge to command the boat safely and are aware of the law governing colision avoidance at sea.
A letter from a sailing club is good also.
Remamber it takes TWO PERSONS to have knowledge.