Explain ACID and transaction isolation levels

Explain what each letter of ACID guarantees, then walk through the standard isolation levels (read uncommitted, read committed, repeatable read, serializable) and the anomalies each allows, such as dirty reads, non-repeatable reads, phantoms and lost updates.

Apply it to a booking system that holds seats for a few minutes: which isolation level or locking would you use to never sell the same seat twice, and what does it cost?