Expedia.com Informative - Customer service-receipt and Thank you points
Don't ever book through this agency. The receipt that these guys give is absolutely useless for claiming frequent flier miles. It does not contain codes necessary for airlines to credit your frequent flier account with mileage. I had traveled on Alitalia and wanted to claim Skymiles on Delta Frequent flier program. Delta does not accept their receipt and Alitalia won't give receipt for past travel since I booked through Expedia. The receipt that Expedia gives does not give the codes necessary for Delta to verify my claim. So I am stuck. Expedia's customer service was no help. They asked me to contact Alitalia for a receipt and did not take responsibility for this even though the booking was made through them.
I booked through Expedia because they promised to give Thank you points on my Citicard account. Never received them for the airfare purchase. Apparently you have to purchase other activities such as car, hotel etc. in addition to airfare before they will give you Thank you points for air travel. But they don't tell you that during the booking process. They tell you that after you have paid when it is too late. Buyers beware. Read the fine print. These guys are not worth the $10 you would spend on their booking fees. Research their site for the best fares and then buy directly from the airline.