Being a born & raised Greek, and having spend 9 years of my professional life in the UK, I have developed an inner "greek-scam" detector which I use every time a fellow countryman tries to "pull a quick one on me".
One of the favorite "quick ones" has to do with MONEY. It doesn't matter if it's small change or large amounts, the fact is that Greeks are a bit complacent regarding money-handling obligations towards the others.
Here's a list of examples from my personal experience:
not giving back the exact amount of change
not honouring the date a debt has to be repayed
overcharging or charging for items not purchased
shop windows: placing a non-representative item price, in order to attract attention
not stating the correct price for purchase of a certain item
not mentioning discount options
not accepting return-for-money obligations, for faulty (or misleadingly described) goods purchased
... and so on so forth
I'm not a trigger-happy person when it comes to money-related problems. I accept delays, excuses, or reactions due to exceptional circumstances. I won't rub a "scam" into the scammer's face, if I sense that his motives are purely out of survival, not greed. But when my "scam detector" smells "rip-off" or "couldn't-care-less"-ness, then I demand that things are done 100% right, NO MATTER WHAT.
Here's a small tip:
always ask for the price prior to purchasing or consuming something. Though it’s not a widespread issue, some greek merchants might tacitly increase the price as soon as they see that you are a foreigner! You’re also entitled to get a receipt immediately after the purchase, otherwise it is your legal right to not pay for the goods received
Conclusion: when you're being served with a "money-scam" behavior, stand your ground!