So here's a devious thing that web sites are doing as told to me by Tracy about her friend.

The site will store cookies when you visit and quote you a price while you are shopping. Then when you go back, the price is always the same or higher. They never show lower prices after you have browsed them once. So her friend was trying to find airfare and got a price but wasn't that happy with it, so she waited. Later she went to a different machine and got the same exact flight for lower. Then browsing with her own machine again she couldn't get the low price again until she deleted her cookies.

Sounds like the stuff of urban legends, but of course it's pretty easily doable, and it could make the site a lot more money, so I'd be surprised if no one had tried it.

The moral of the story. Try deleting your cookies every once in a while to see if you can get the price you think you should get.