Instruct: Classify Amazon reviews into positive or negative sentiment
Query: a worthless product

I had been using Petco's Grass be Green for a couple of years for my male shih tzu. It worked beautifully---no more brown spots at all, with no side effects for him. When I ran out, about a month ago, I decided to try GrassSaver because I could get it online more quickly than I could get to the store. Suddenly realized my lawn has numerous brown spots once again. I am headed to Petco today!