"Rate Parity" - what a joke!
Expedia owns TripAdvisor.
If you go to TripAdvisor you will find links to hotel sites scattered throughout their pages.
What TripAdvisor doesn't tell you is that most of these sister web sites have an incestuous relationship through their cookies.
You get one quote from Tripadvisor it offers to let you compare prices and the prices are all within a dollar or so of each other. Delete the cookies as you switch from one site to another and then you see some action!
Another way these outfits can rip you is by pricing individuals, i.e. per person, when the rooms are sold in the country as rooms. This means they can really increase their take.
Hotels.com and Hostels.com have another wrinkle. They accept your reservation and charge you a deposit. These 'deposits' are actually their commission for the booking activity - in other words the hotel or hostel sees squat of this money.
They simply send an e-mail off and say Mr. Smith is arriving on so and so date for three nights. The weakness is that the web site relies on the hotels to advise them if a room is available for the whole block of days. Unfortunately they often don't.
Another problem arises is when a customer arrives at the hotel and the front desk, live and in person with only one room available. The question is: does the hotel sell the room and get full price or pass on the live customer and hold for a maybe? Often the choice is for the live customer which means that if the Hotel.com reservation turns up there is no room available.
So Hotels.com complains to the hotel and they say: E-mail, what e-mail?
You would need a genealogy program to detail all the inter-relationships between travel companies, it is simply unbelievable.
And never use someone like Expedia for flights, they get a bonus for selling the left-over seats.
I'm not in travel as a business, but do yourselves a favour - use your local travel agent, at least you can scream at them when things go wrong.