Just explain that hair care is more nuanced than most people imagine - that every head of hair is different and responds differently to different products and techniques. Top it all off with a pleasant "Thanks but no thanks for the advice."
3b/c?

Ringlet Fandango! ... Where curly ideas roam free

* 2 blogs this week: Pictures of My (Sorta) Big Chop! AND Turn a Nightmare Product into a Dream* My Albums