Re: Danger - greek taxes
Here is the relevant EU tax policy with regard to non-EU citizen boats in EU waters. Follow the requirements or pay. I don't know if member countries can impose additional fees but, looks like the original poster did not do their homework before entering EU waters.
Some Frequently Asked Questions about the rules for private boats - European commission
1970 Havsfidra 20 by Fisksatra
On the Delaware River at Fox Grove Marina Essington PA