Hi @Luis24
If he has two reviews already, he knows how it works. He is asking to visit the flat in advance in order to make a private deal with you outside of the airbnb system. This is evidenced by him circumventing the system to send you private info such as his phone number, and asking you to send him information written in a way to bypass the security. The reason that he is asking you to write the local currency in letters/words and not numerical values is that a big number appears to the filters to be a phone number, and it's redacted.
It's your business, so you can do what you want, but his communication with you raises red flags for me, and I'd be very careful. I would not allow him to preview the flat, and I would not allow him to book directly. If he came to you through the Airbnb system, then you should honor the booking within the system. If he was referred to you privately from a friend, for example, then I think it's ok for you to book him privately, but of course that means that you have none of the Airbnb protections.