Most modern browsers also have a feature to allow users to indicate if they want the browser to not send cookie information to the server. You can search for InPrivate (IE), Private Browsing (Mozilla/Firefox), Incognito (Google Chorme), etc. This feature will also prevent the browser from saving form or password information, etc.

Even more modern browsers also have a do-not-track feature that specifically tells a website that you don't want your data to be tracked. Of course, each specific website can decide whether or not to honor the browser's request not to track the user.

Getting back on topic as for the practice of increasing the fare for elite travelers or people who are logged in... Is this actually confirmed? If so, wouldn't aa.com consistently run into problems with their "best price guarantee"? Seems like an easy way to get $50 discount codes with every purchase on aa.com.