Does anyone know what's the average value growth in the greek islands?

I mean when I see commercials talking about figures like 20 or 30%
this can only be a short term local demand,
I want to promote and sell properties and own land plots in Crete but not
mislead clients, in fact I make the case both for and against Greece as it appears
to be ridiculously expensive market and poorly regulated, of course if someone
likes our culture and country they will still buy here.