How to tell if a travel site is legit?

You could check what country they're headquartered in and if they have a Better Business Bureau (or local equivalent) rating/listing. You can also check online for reviews or even ask on Travel.SE if your initial search doesn't bear results.

In terms of recourse if you're duped (assuming you mean they took your money but didn't give you tickets), after contacting their customer support to make sure it's not a fixable error, you can file a credit card chargeback to get your money back and complain to the BBB or a similar local business registry regarding the company's fraudulent behavior. Documenting your experience on a high-traffic travel forum online will help others avoid getting scammed, too, as they might see your story when they search for the website.

Further to my initial comment: "they had the lowest prices by far" ... the biggest red flag there is for buying airline tickets online, buyers need to research a variety of sources and compare pricing. With airfares, prices are set by the airlines and as such most online booking sites will show the same airfares.

When you come across the website that has appreciably lower airfares than anyone else, then you need to be suspicious and look into them more. There are four common scenarios that could be applicable: 1) They are a consolidator with legitimate discounted fares; 2) They are showing the lowest fare for that city pair not whats available; 3) They are selling tickets that were "bought" with frequent flyer miles; 4) They are simply con artists and criminals.

Consolidators are becoming less common, as airlines don't really give them that huge of a discount anymore and people can find similar airfares online. They usually mention that they are consolidators and you will likely see notices about the restrictions that come with their fare, such as zero frequent flyer miles. They are also the primary advertisers in the Sunday travel sections of big newspapers. They will usually have their seller of travel licenses posted for several states. They are usually right up front about the fact that you need to request your flight and they will confirm it later.

Businesses selling frequent flyer ticketed fares are pretty easy to spot because they almost always push their killer offers for business class and first class airfares (like $2500 for a $9000 first class seat). These folks, same as consolidators will tell you to submit your request and they will confirm it later. But these tickets are against airline frequent flyer policy and you could be denied boarding on your first flight or even billed for the flight.

Number two is basically bait & switch, but most of these businesses have things worded such that they aren't really guilty by the letter of the law (hence the police comments about not being able to do much).

Determining if they are legitimate, after you have been suckered in but before you push the "book it" button...

• Do a quick search of the bigger air travel forums - flyertalk.com, tripadvisors.com's air travel forum.

• Do a quick search on google for Problems with Company Name, etc.

• Most states allow you to look up business licenses for "professional" categories under which travel agencies usually fall.

• Check with the BBB for feedback on the company.

Unfortunately, just because they show up on mega-search platforms like Kayak.com, does not mean they are 100% above board. Businesses can be "legal" and also "unethical".