Buy only through the direct service provider!!!
We bought tickets in January for a trip in June, from Oslo-Bergen-Oslo. We paid for a 2-bed-cabin fully in advance. In march we were informed there were no more cabins available and we either could cancel or take regular seats. On the website the cabins were still offered though! Since we had already booked all other things, there was no other option than take the regular seats. We were refund the difference. Still, it felt like misleading advertising. And we tried to make an upgrade when we were in Bergen (costed a lot more) from the regular seats to a cabin, so they were actually avaialble at the end. Once we were in Norway, we were told many times that Rail Ninja seems to be a scam. I was glad that we at least got regular seats. Please buy only your tickets in the websites from the transport service providers.