Kayak.com, a traveling website, actually really responded to feedback i’ve sent them.

Hi,

Those are good suggestions. 
 However, since we don't actually sell anything, 
we don't really know if you ended up booking or not.

We actually do include a link so your friend can search for the flight and book it if she wants.  
But the booking links themselves are short-lived and tied to sessions, so we can't easily send the exact booking link without first conducting a search.

Thanks for searching with KAYAK.

Best Regards,

Bill, chief architect

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when sending an email to a friend about a flight,
you should include a link so the friend can book
this flight as well; while booking you should note
to him if i ended up booking it or not

I’m finding the website really useful.

http://www.kayak.com