Why do flight prices change so much?

Related questions

1. Is it cheaper to use travel agent?
2. Do flight prices drop at last minute?
3. Are Spirit tickets cheaper at the airport?
4. Why are Spirit tickets so cheap?
5. What are spirit fees?
6. Do plane ticket prices go down?
7. Can travel agents get better airfare?
8. What days are the cheapest to fly?
9. How much is a travel agent fee?
10. Are tickets cheaper at the airport?

Tags

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5. #different
6. #purposefully
7. #every
8. #offer
9. #least
10. #prices
11. #because
12. #airlines
13. #expect
14. #sales
15. #lower
16. #flight
17. #fares
18. #might
19. #operate