The first thing that should set an alarm off is when you receive something you didn't ask for. If you receive an email, phone call, or mail saying Congratulations you've won....The first question you should ask is where did they get your name and information from? Did you actually enter a contest for that company. These type of offers are always gimicks. They aren't going to give something away for nothing. The catch usually involves a Time share sales pitch which you will have to spend your vacation time listening to. They will involve lots of extra add on cost of taxes, fees, etc. They will push paying for upgrades because what ever they are pushing won't be available on the date you want, but for $xxx dollars you could have a different one.
Don't give any of these type of offers the time of day.