I was looking at them too for a minute. They showed up on my Kayak search, beating the aircanada.com fare for my fairly last minute flight by about half. Then I started reading the reviews on them, and wondering the catch on them being almost half of what every other competing site was offering. Ended up booking the trip as an award, but still not sure about using airfare.com.

I assume they are a consolidator if they are selling seats like that, and would assume they would be in the Tango bucket. Though I should stress that i have no experience in bookng tickets through them. I always know that perhaps its not the best place to buy a ticket if googling them results in finding several very negative reviews involving fraud, overcharging, etc. too easily.