Some people just reject a negative comment instead of dealing with it. They fail to recognize this golden opportunity as a way of promoting their product and convincing the writer that they just may be wrong. It is always better when they say this to you and not about you out in the community. Negative comments can have positive outcomes too.

When someone criticizes your product accept what they are saying graciously. Just like you they have the right to express their opinions. Tell them how sorry you are that they feel that way and then promote every positive point your product has.

If you are getting sales you could mention to them that your ? number of customers have been very happy with your product. If you have any reviews about the product then refer the critic to them or cut and paste a couple of the best ones into your reply. Never miss and opportunity to promote your product and convert a skeptic.