My theory on where the "clear cookies" myth comes from is on many sites if you proceed too far down the purchase path then the ticket is taken "off the market" for you while you complete payment. If it was the last cheap ticket available and you abandon the purchase, the ticket will not always immediately be released back onto the site. So it looks like the price has gone up if you check again. If you wait (20? 30? minutes), the original transaction times out and your cheap ticket is back on the site. Not sure if this is the same for BA.com