I booked a United flight from DEN to SFO in late December. Immediately after booking (less than 5 minutes), I realized that my return trip was in first class. I wanted coach and didn't catch that. I canceled my flight, was charged a $100 change fee (my penalty for being stupid) and re-booked the ticket in coach both ways. The difference in fares (after the $100 fee) was $300. Read more »