I've been travelling in Spain, and short story, I got scammed but was handed 30 euros as "change".  If you want the full story because your curious or think its critical for context you can check my post history, where I posted about the experience.

After I posted said story, a redditor pointed out "that 20 euro note he handed you is almost certainly counterfeit". 

I immediately panicked.  I looked up how to check if a euro is fake.  From what I found, my bill seemed pretty real but some of the descriptions of what I was supposed to look for weren't clear to me.

So I figured, if it's a fake, it's a high quality fake.  I then to decide to spend it somewhere where I think it's most likely to go unnoticed if it's fake.  I find a local grocery/convenience type store to break it.  I go and spend it without incident.  

I felt sort of guilty because I might've just screwed a small store out of 20 euro.  I'm not sure if the store will have to eat that cost or the government.  I obviously feel guilty about the former possibility.

I rationalize(d) it by saying, well it should still be my euro to spend even if it's fake.  In a way, the scammer stole from that store, not me.

However, it always seems to me if you have to rationalize it, your in the wrong.  

I'd like to clarify that I DON'T know whether the bill was fake or not.

So what does reddit think?