A good article over at about.com about 10 things you should be on the lookout for that could indicate the travel "deal" you're considering is actually a scam:

Advance payment is required without a written contract
Transactions by courier service rather than post office
Transaction can only be carried out by telephone
Offer is for a "limited time only"
Different names for travel provider and seller
Hotel names, airlines or other vendors not disclosed in writing
A price far below market value
Offers to make you a "travel agent"
Hints of "Split Pricing"
Frequent use of words such

There are a lot of good travel deals out there, but you also need to be wary of those trying to separate you from your hard earned money.