Shares of TripAdvisor Inc. are down 0.8% in premarket trading Wednesday after Guggenheim analyst Jake Fuller downgraded the stock to sell from neutral. He wrote that online-travel agencies are prioritizing margins over room-night growth, "which has undermined meta channel growth and may not be done." Fuller also sees a "tough competitive backdrop" now that competitors are spending more on ads and TripAdvisor is pulling back spending. "Trivago should spend nearly two times the amount we project for TripAdvisor," he wrote. Fuller now has a $40 price target on TripAdvisor's stock, which is up 6% over the past 12 months, compared with a 13% rise for the S&P 500