I used to book few flights and vacations with expedia.ca few years ago. Tried to do it again and had a very bad experience. I was looking for some flights to Europe for this summer. I managed to find some good deals for around $7000 for 4 tickets, went through the entire process of providing all details for all 4 members of my family, got to the final step providing my credit card and all of the sudden I got message the price has changed to $9500. I thought that was a bad luck and tried again with slightly different flights, and the same happened. What a scam. I went and booked my tickets with Lufthansa directly with no problem and the original price of ~$7000.
Stay away from Expedia. Unfortinatly Booking.com and other similar sites are pretty much the same, it looks like it is the best to go with hotels and air companies directly.