They bait and switch ticket prices
As many others have said, they use a bait and switch approach. They quote a low ticket and then show it has pending. They will call you and tell you that ticket is now gone and the prices have gone up. They also try and charge you more for a carry on bag when it's an airline that doesn't charge for carry ons. I assume they hope people that don't fly regularly will not know any better. When I tried to make them provide a ticket that was quoted they said I would need to use another form of payment because they don't take Capital One Visa. They take Visa, just not that Visa, not to mention it was accepted fine on their website. Clearly they knew they could not fulfil the ticket at the price quoted and they needed a way out at that point. They are totally a scam, I would highly suggest using more reputable services.