Another thing I found out with Expedia was that bargain airfare often did not include taxes and booking fees. So if they advertise $200 roundtrip, you will find that by the time all the taxes and fees are added in, that $200 airfare was a heckuva lot more expensive than if you booked directly with the airline.
They are good to compare prices and that is it. Plus the big turn-off is that you are told to buy this fare because only x-number of seats are availible and then go to the airlines direct and see they have more then enough seats.