I look at multiple reviews if possible to determine whether or not I will buy from a company. I tend to look for patterns, either good or bad, in reviews. There are some cases in which I will overlook popular opinion and just use a product that I know works for ME. For example, when the company that makes California Natural was bought out I continued to feed it despite all of the negative hype surrounding it because it had served us well. Sally is allergic to TONS of things so there is only a handful of kibble she can eat, and California Natural is one of those. I switched her to a different kibble for a while, just because, but will use CN again.
I understand that quality issues can happen in even the best of companies, but the real test is how said company handles the issue. If they bend over backwards to fix their mistake, great. But if they were difficult, unfriendly, etc, I would take my money elsewhere. I work for a company that is known in our industry for its excellent customer service and I see what a difference that makes in the grand scheme of things in the business world.