For me I respond based on how the advice is given, how often and how insistent they are. If someone recommends to me "she who will not be named" I have to admit I do not hold back on saying what I think about her.

So normally I will just say "I am not comfortable with that" and if they push it I become less polite. I had someone harping on about how unsafe co-sleeping is and I ended up snapping back at her "well babies still die in cots by themselves, I think you should back off."