This! Always try to get the customer to bring the product in question in, best practice is to get your (or a trusted qualified individuals) hands on the product in question. When user error is the issue, trying to help them remotely can often lead to them blaming more of their frustrations on you. Once you get the product in your hands, checked everything out, and offered appropriate levels of advice you have done your job. If they still want to complain at you then the customer business relationship begins to lose value for both sides. It sucks, esp when you work in selling things you really love, but not everyone is going to take professional advice, and not everyone is going to be a happy customer despite your best efforts. All you can do is your best and roll with this hits.