I took the most exception at this comment for some reason. I guess because it seems like a serious suggestion instead of an example of what I understand as arbitrage. Maybe because it seems the most hand-wavey of all the suggestions.
Yeah, you can sell bottled water on the beach for more than you paid but, I think it's dubious to say that you can make decent coin in the long, or even mid-term. When I think "decent coin" I think of an income that can support my lifestyle and family.
Valuable as a way to learn about business? Sure.