I'm fairly sure that they don't as I have seen other sites with lower prices quite often. The thing is that normally those "price guarantee" places have a whole lot of stipulations that have to line up just right in order to get the guarantee in the first place. I've tried a few and it's just such a PITA that in the end it's not worth the few extra bucks.
Also EF has great shipping rates, and their free shipping min. purchase is prety low too. They also ship quickly and I KNOW their shipping will be discreet.
When you add that with the fact that I feel safe knowing that if I get a defective product I can return it and that I can read all the reviews so I know what I am getting, I really don't mind that EF is sometimes a bit more expensive. EF also offers awesome sales and discounts!