By Kirk Miller In a gigantic loophole that certainly damages the pocketbooks of writers, Amazon is under fire for allowing the return of purchased e-books after a week. The shopping giant’s rather generous seven-day return policy does offer this caveat: “If you have a high rate of return requests in your account history, the self-service refund option might be blocked.” But the language there is so vague, and it doesn’t help the writers — particularly self-published writers, who actually might end up with a negative earnings balance, according to NPR. Why a negative balance? When an Amazon cus…