Remember, as web developers we are paid for our expert advice. If a client doesn't accept my advice, I make them sign a waiver. Psychologically, it emphasizes my position with the client. And it protects me from future backlash when the site performs poorly on Google, etc...
Interestingly, when a client is asked to sign a waiver, they sometimes acquiesce and do what I recommended in the first place. Something to consider...
Nancy O.