Originally Posted by jackal

I'm pretty sure that EF isn't going to publicly comment on their vendor relationships (I wouldn't if I were them). I'll point out, though, that EF obtains all of their information legitimately via paid subscriptions to various and sundry GDSes (the same systems used by most travel agencies). Thus, their information is very accurate and stable but can be limited if the airline doesn't publish a specific class on the reservation systems. In most cases, I don't think it's because the airlines are actively masking any information from EF itself but rather that they simply don't publish the data on the GDSes at all.

Many of EF's competitors obtain the information from publicly-available free sources but are technically violating the TOS of most of those sources, since those sources invariably prohibit any form of screen-scraping or other types of data harvesting. Whether that is objectionable is left up to you to decide, but note that EF's competitors tend to have to play a cat-and-mouse game with the data sources when those data sources change their interfaces or try to block the products from accessing their data.