Call them out and ask why, they would go to such a position out of fear, fear of your success, always remember boys and girls if they are talking good or if they are talking bad, they talking, and that gives you a beautiful platform to address the situation and receive great deal of free advertising  to benefit from, controversy is very popular and it sells just because it creates interest, so don't get mad if someone slams your company, get rich by the opportunity to explain why the individual failed to realize the incredible benefits your service or product provides, and one important lesson is to make sure they actually used your business and paid the price to give an opinion.