After this indie bookseller posted about an unthinking mystery customer, the internet read this rude customer to filth. On her Twitter account, bookseller Rebecca George shared the real-life background of what goes on behind the scenes at a small business. It's not like the mega-stores and online giants — every penny counts in small business, and people's livelihoods are on the line. George tweeted about a customer who unthinkingly returned a large order, and wrote about the cost it was having…