How do sites like Trivago make money?

Related questions

1. How do you get listed on TripAdvisor?
2. What percentage of Yelp reviews are fake?
3. Is TripAdvisor a public company?
4. How do I list my travel company on TripAdvisor?
5. Is TripAdvisor safe to use?
6. Are TripAdvisor reviews fake?
7. What is the meaning of TripAdvisor?
8. Are yelp reviews fake?
9. Why is TripAdvisor important?
10. How many reviews are on TripAdvisor?

Tags

1. #hotels
2. #charged
3. #called
4. #sites
5. #earns
6. #whereby
7. #listed
8. #booking
9. #revenues
10. #deals
11. #which
12. #selecting
13. #clicks
14. #basis
15. #first
16. #commissions
17. #users
18. #trivago
19. #hotel
20. #based
21. #click
22. #revenue
23. #referral