Reviews are marketing you do not control, which is what makes them credible.
GETTING THEM
Ask, once, a week after delivery. Most satisfied customers oblige when asked directly.
Make it easy: link straight to the product's review section.
Do not offer payment for reviews. It is obvious and it undermines the point.
MANAGING THEM
Hold reviews for moderation at first, so nothing abusive appears unseen. Restrict reviews to verified purchasers to prevent most fakes.
RESPONDING TO CRITICISM
Reply calmly and specifically. Acknowledge what went wrong, say what you are doing, and offer to sort it out.
Every future reader sees the reply, and a well-handled complaint reassures more than the complaint discourages.
Never argue publicly. Move it to a private conversation and return to say it was resolved.
WHAT TO DO WITH THE FEEDBACK
Patterns matter more than individual reviews. Several people mentioning sizing means your description is wrong, not that the customers are.
WHAT NOT TO DO
Do not delete genuine criticism. A page of unanimous praise is less believable than a mixed one answered well.
