Sales of Green Works have fallen from $100 million to about $60 million a year, and those of other similar products from major brands like Arm & Hammer, Windex, Palmolive, Hefty and Scrubbing Bubbles are sputtering. “Every consumer says, ‘I want to help the environment, I’m looking for eco-friendly products,’ ” said David Donnan, a partner in the consumer products practice at the consulting firm A. T. Kearney. “But if it’s one or two pennies higher in price, they’re