Either you will get a booked ticket or you won`t, and the airline will know very quickly if you are. Determine whether that is successful as quickly as possible. If you don`t get a booked ticket, contact your credit card company.

I think the complaints I have read about such sites (not necessarily these ones) are of this nature: I booked for $800, but the site came back a day later and said the real price is $4000. Then, depending on the story, the user`s credit charge is charged for a larger amount or the user gets no tickets at all.

So if I really wanted a ticket from these sites, I would take careful note of the T&Cs, save copies of them, and figure out if I had time for Plan B if the ticket purchase failed, and be ready to challenge if charged for a larger amount.