Investors short-selling Shake Shack Inc (SHAK.N) may have made money over the past week, even after paying exorbitant interest rates to borrow the stock. In a week when the S&P 500 lost 5 percent over three days, Shake Shack’s example shows that sophisticated investors can profit in down markets but often do so at a high risk. Since its initial public offering in January, Shake Shack has been wildly popular with Wall Street and with consumers, who wait in long lines for its indulgent hormone- and antibiotic-free burgers and sides.