I'm new here and I would like ask your opinion.

[Sergiu3]

The situation. The gues check in all good.

After a 1h I got a text from him. "didn't know someone else will be in the apartment."

He cancels the reservation and left. Now he left a bad review and asking for money.

how is the right way to fix everything? 

[Lawrene0]

No need to fix anything, @Sergiu3. No one will pay attention to that review. It is clear he didn't read the listing. A few more good reviews, such as you have been getting from your other guests, and it will be buried completely. Getting a refund is between him and Airbnb, and obviously it didn't go his way. It's never fun to get someone like that guest, but it's nothing to worry about. Stand your ground. He can ask all he wants, but there is nothing he can do to you.

[Emiel1]

Hi,

Your listing says it is a private room in a condomium. Allthough a little bit confusing stating : 3 guest (but bedroom sleeps 2).  A guest should read your listing carefully. Even the guest's review is not clear about his expectations. Ask the guest to contact Airbnb and let them decide about refund. My personal opinion is: refund should be rejected. Maybe update your listing on details, so future guests will not have wrong expectations. Best, Emiel

[Linda108]

It is never fun to go through this, @Sergiu3, even if you are in the right.  I agree with both @Emiel1 and @Lawrene0, in that the guest needs to battle it out with Air BNB.  However, every negative experience is an oportunity to look at the listing and tweak it.  I would add pictures of the "shared space" and add the captions regarding how the shared space is used.  I recently had a booking and then a cancellation because the guest did not realize the space was shared.  Besides the "private room" and pictures and reviews, this guest thought she could get an entire house for a third of the usual price for an entire house.  Sigh...

[Hugh0]

Don’t sweat it. Idiots leaving bad reviews because they don’t read listings is par for the course

I will receive a bad review from a guest today because they checked out, did not message me and took the keys.

I had to contact them to return the keys. No apology and they were pissed at me.

In return I will leave a review that will make them as welcome as toxic waste.

[Fred13]

My favorite motto also Linda: "Every negative experience is an oportunity to look at the listing and tweak it."

If anyone gets confused about anything, immediately spell it out that much more explicitly in your description, if it warrants it, so no one can claim 'confusion' (aka ignorance).