The thing about the Internet is that EVERY MENTION MATTERS. Some companies have special employees posting reviews on multiple forums (actually, nearly all IT companies do this and quite a part of every popular forum community is such emloyees).
Why is it done? The more times your website name is mentioned, the better. Search engines do not count emotions, they count only matches of keywords. Good review plus bad review are simply2 reviews.
Therefore, both positive and negative replies do the same job - they promote your service. And if someone does it free - that is just great! It will only result in higher ranking and more customers
To a certain degree, of course.
Customer experience is really important, as satisfied customers are your revenue generators. Thus said, having a person tracking customer experience issues is a good idea.
Multiple software tools allow tracking your website name matches on the Internet. In case 1 client posts 1 negative reply somewhere - it is no big deal. However, someone really angry at your service may start posting bad reviews very wide - the situation you were talking about, OP.
The solution, the way we see it, is to try contacting the frustrated client by any means possible to deal with their situation, give directions regarding resolving the case or issue them a discount/refund.
If there is a possibility to reply to their accusations with detailed explanations and useful advice - use it! Just do not criticize, don't tell them they are wrong - just show the way out (and mention your service one more time, of course
This way even people reading these bad reviews will see the way you deal with such cases - calmly. efficently, friendly. They will be able to judge the situation from two sides, not only from bad review, but with your good response, too.
The best way to advertize good service is to show it in action, IMHO!