Exactly the same as when I ask my friend who's passionate about wine for his recommendation for a £15 bottle of red, and he'll happily waste 20 minutes of his day writing a list and sending me links. I know the pleasure he gets when I message and go "thank you! This is amazing!"
Also just to add - this is exactly why those "get paid to recommend things to your friends" startups never work. Because the minute we know that the 'friend' on Facebook who's shouting about the great bottle of wine is getting paid £1 per sale we deliberately don't buy it. (As opposed to the "next time you're in Tesco, pick up a bottle of XYZ, it's great" message - when we probably do.)