Always make a legal search of the property. Find a local trustworthy lawyer to help you with that.
Find a good real estate agent that you trust. He/she will be your contact and he /she will provide you all the guidance you need through the sale process.
Ask for the property files and make sure you check them thoroughly with your real estate agent and your lawyer.
If you are not Greek , but you are a European citizen, you have the same rights as the locals. Just get your Greek tax number and you are ready to buy your first property in Greece!