Respond within hours rather than days, even if the response is only that you have seen it and are looking into it. The period between somebody complaining and hearing back is when a private annoyance becomes a public review, and the length of that period is the single variable you most control.
Acknowledge the specific thing rather than expressing general regret. Sorry you had a bad experience reads as a formula and signals that nobody has read the detail. Naming what went wrong, in their words, demonstrates that you understood, and that demonstration does most of the work of the apology.
Resist the instinct to explain why it happened before addressing what happens next. Explanations sound like defence to somebody who is annoyed, however accurate they are, and they invite a rebuttal of the explanation rather than a resolution of the problem. Lead with the remedy, and offer the reason afterward only if they want it.
Take it out of public view early where it started publicly, but respond publicly once first. A single calm, specific reply that names the issue and offers to continue privately does more good than the complaint did harm, because the audience is the next twenty people reading rather than the person complaining. What they are trying to learn is how you behave when something goes wrong, and an argumentative reply answers that question badly and permanently.
Decide what you are willing to do before the conversation rather than during it. A refund, a redo, a partial credit, or an apology with no remedy are all legitimate depending on the situation, and deciding under pressure produces inconsistency you will regret. Knowing your position in advance also lets you offer it immediately, which is what makes the resolution feel generous rather than extracted.
Understand the arithmetic of the remedy. The cost of resolving a complaint generously is almost always smaller than the cost of a negative review that sits on your profile for years, particularly for a first year business with few reviews where one critical entry carries disproportionate weight. That does not mean conceding to everything, and it does mean the calculation is rarely about the immediate amount.
Some complaints are not resolvable and recognising them saves considerable time. A customer whose expectations were never achievable, who escalates regardless of what is offered, or who is attempting to obtain something for free. In those cases state your final position once, clearly and without hostility, and stop negotiating. Continuing produces worse outcomes and consumes attention that belongs elsewhere.
Then find out what allowed it, because a genuine complaint is information you would otherwise have paid for. Most originate in ambiguity rather than failure: something that was not stated, a timeline nobody confirmed, or an assumption both parties made differently. Fixing the underlying gap prevents the next twenty rather than the last one, and that is where the actual value of a complaint sits.
Keep a short record of every complaint and what caused it, even the ones resolved in a single message. Individually they look like isolated incidents, and across a year the pattern is usually obvious and usually about one or two specific gaps in how you communicate rather than in how you work. That record is the cheapest quality information a small business can collect, and almost nobody keeps it because each individual entry feels too minor to write down.