Too Good to Be True Contests on Facebook
The real deal:
A scam one:
Many of these pages are there to build likes, then later change the name to something else and sell it to others with ready likes built in.
If you've liked a page to win free Disney tickets, a cruise, or anything else that just seems too good to be true, I suggest you go into your Activity Log, click on 'Likes, then "Pages and Interests', then scroll through to make sure what you've liked is actually stuff you're interested in the page. Remove yourself from anything that doesn't interest you.