This whole problem with Greece came to light when some government employee took a look at a satellite photo of Athens and saw all the swimming pools in the backyards. Greece had a tax on building swimming pools, and no one was paying it. That started the whole house of cards to start falling.
Also...when building an apartment building in Athens (and anywhere else in Greece) ...with a permit for 4 floors....the elevator mechanism needs a shelter on the roof....the technician needs a wash room....and bathroom.....and a store room for spare parts....soon the 5th floor is a lux penthouse ....and of course not reported to the tax guts.