While such negative tactics may help a company grow in the short term, in the long term such a company will fail. Most successful companies get a large portion of their business from repeat customers and most people like to do business with people they trust.
If I am a customer of X company, and I know that company Y is using negative tactics or dirty tricks to discredit X company, so that I sign up with them, I will avoid using them in future. If I become a customer of Y, I will always be worried that company Y is trying to harm my business, since I have got first hand experience of their business techniques.
There is very little to differentiate between the internet companies today in terms of technology. The way you do business is important. For long term success, a company should have a win win relationship with both their customers and vendors. There is always scope for growth and all the parties involved are winners.