In Greece the Ministry of Development has an online database which includes Gas Station location and prices. Prices are being updated by Ministry personel and the gas station owners themselves.
Its a great source of info that's up2date (i checked some randomly and they were updated within the previous 5-10 days) and its usable as its from a public entity.
I think it would be great if Waze would incorporate it to for Greece (which currently lacks Gas Stations overall) and furthermore continue allowing users to edit the prices and either show the latest price available or just mark whether this is the "official" price or the crowdsourced one.
Now for the catch. The site is available here: http://www.fuelprices.gr/
a) Its in Greek. Only in Greek.
b) Its one of the poor-est designed websites. Not sure how the data could be crawled and how a sync could be setup. It is doable however because quite a few 3rd party sites in Greece are doing so.
Anyway, if there is interest i'd be willing to help. At least we could use this db to jump start gas station location and leave the price sync-ing feature for later.
I'd be more than happy to support and we can ask other users from the (small) Greek Wazer community to help also.