Too good to be true? I buy bitcoin on Coinbase, and then turn around and sell it on Localbitcoins for a 20% markup. I'm making so much money, and it's so easy. Why are more people not doing this? Am I not understanding something?

I figured not requiring validation makes me more attractive to buyers, but with a 20% margin, I could afford for one in five of my buyers to be scammers, and I'd still break even.