Reviews are used by everyone, including those on your email marketing lists, to assess if a product is worth buying. In order to ensure customers are not put off you need to have a process to manage negative reviews.
Ensure the reviews are read critically by someone aware of your policy. That means the good, the bad and the indifferent ones. They will be a resource as to how any product is being received project plan template.
Their task is to deal with negative reviews, yours to issue the guidelines. The first thing they need to work out is whether any action is required on your behalf. Doing nothing is a valid response if it is justified. Remember that a nonsensical review will be ignored by most customers and you do not want to be making the problem worse.
Any review that requires a reply should be addressed immediately. That doesn't mean reply in haste but to consider the best form of reply. Ensure there is no intent for payback. If you are reasonable and polite to someone who has been rude, a customer will probably assume your response to them will be at least as considered. Accept that if a review is rude, it might be because the customer has difficulty expressing themselves.
Consider that the fault might be yours. If it is, admit it and suggest a remedy. An apology reassures as does a promise to correct an error.
If the reviewer is completely in the wrong, don't use them as target practice. Point out where they are incorrect and leave it at that.
Stop when you have said all you usefully can. Continuing an argument when the other person isn't listening is pointless and will put off potential customers. Which brings us to an important consideration:
You will not only be judged on reviews but also the way you respond to them. It is pointless suggesting customer relations are important to your company and then telling a complainant to go take a hike as the law is on your side.
Even customers on your email marketing list need reassuring. They too will check out the reviews. Be sure you don't frighten them away.