"A typical business hears from 4% of its dissatisfied customers." - Ruby Newell-Legner, "Understanding Customers"
Negative feedback is valuable because it tells you how to fix your business. Most dissatisfied customers won't bother to contact you, so the ones who do deserve consideration. The more clear and detailed the complaint, the more the company should analyze it. Sometimes what's actually being shared are the symptoms of a much deeper problem.
Only a fool ignores criticism.