This one of most referenced quotations with which I'm familiar: "To give real service, you must add something which cannot be bought or measured with money, and that is sincerity and integrity."
I like it so much, I used to use it as tag line on my business emails.
As it was attributed to *a* Douglas Adams the first time I saw it, I gave it that attribution and assumed it was the Douglas Adams who wrote Hitchhikers Guide...
Then I saw it attributed to a different Douglas Adams. (I forget where I saw that.)
This quote appears at http://quotationsbook.com/quote/35928/ and is attributed to the Hitchhiker's author, but without an actual reference.
Does anybody know where the quote comes from?