If the person purchasing the ticket isn't flying, or isn't going to the airport to show the credit card, then they should not purchase the ticket online through UAL.com.

Some other airlines are not as strict, for example Delta allows you to purchase for others if you are one of the people traveling or have the same last name as at least one of the people traveling.

Once I did see somebody in next to us in line frantically calling their father to come back (he just dropped them off) and show the card because they wouldn't let them by (about six months ago in New York, don't know if that has changed or not)