So I booked my apartment and I found out how Ostrovok works.
For those who don't know:
Ostrovok won't send the credit card details to beds24.
They will send it to you by email in a secure PDF file. You have to have the password to open it. You should receive the password when you opened an account with ostrovok.
If you can't charge the card you can mark that the CC is invalid and then the guest has 24 hours to change it.
If the guest doesn't change the card details you have to mark it again as invalid and then guest has 12 hours to change it.
If he doesn't do it the reservation will be canceled.
Ostrovok doesn't share guests details with you at all. (same as Agoda)
However guest will get your contact details - phone number and e-mail
If you want to contact the guest you have to write to
[email protected], then they will forward the message to the guest.
Regarding the payments. There are two options for guests. They can pay on-line to Ostrovok or directly to the hotel. If they pay to the Ostrovok, Ostrovok will pay you at the beginning of the month (not after every reservation)
Guest can also cancel the reservation if he finds the way to do it. I mean this literally

The link to cancel the reservation is located in the guest's extranet. It is a link that says "cancel the reservation". The font size is significantly smaller than other text and it is light, light gray on the white background

So you really can not see it very well.
I couldn't believe it when I saw it - it is really a stupid way to get fewer cancellations
Hope this helps to those who are new to ostrovok.
P.S. in 2 months during the high season I didn't get any reservation.