Check early in the morning as most airlines' revenue programs are run nightly and lower fares may be available in the morning and gone in the afternoon. Also lower fare seats are not released every day so you need to be patient. Last Tuesday and IAD-TUS on UA was $525 with W fare out and V fare back, On Wednesday morning the price was $424 with W fare both ways, on Thursday $525 fare was back. It pays to be patient and check often and be ready to purchase when the fare you want comes available. Unfortunately, I am planning to upgrade and was waiting for miles to post so I could not take the Tuesday fare. Will wait until it comes available again.