Receiving negative criticism after a groom can be really tough to handle; you put in so much time and effort to do your best work, only to have it degraded by the customer. It's not a pleasant experience but unfortunately it happens at all stages of a grooming career. Here are some tips for handling the situation and moving on:
Is there anything I can do?
Ask the customer what exactly they would like different. If there is anything that can be fixed, like an area being too long, invite the customer back to your salon to allow you to fix it. Apologise for the inconvenience caused and assure them that this won't be the case next time.
If there is nothing to be done...
If the dog was matted and had to be shaved off, advise the customer as to why this was a necessary step to take and what they can do at home to avoid this in the future. If it was a genuine mistake on your part that cannot be fixed easily, say you took the dog a few lengths too short, see if it's possible to make amends by possibly offering a discount on a future groom or a refund and sympathise with the customer.
Can I learn from this?
Although it is difficult to not get defensive, you must remain professional in order to protect your business' reputation. Try to look at bad reviews as learning opportunities, as each one can help you think of ways to adapt and get better. Think, "what can I do differently next time?".
Maybe you could ask slightly different questions when the customer comes for an appointment, to make sure you know exactly what they want? Or, maybe you could ask how the groom looks before the customer leaves, so you can fix minor mistakes then and there?
Just remember to take it on the chin, you can always do better next time!