We booked directly with DIC website which can confirm the ticket faster than other third party website. Staff is prompt in responding to email and helpful.
Go to level 2 at Hanoi train station to use the overhead bridge to reach the correct platform. No escalators nor lift available. It is easy to find where the train is.
The cabin in the train is clean. As we only bought three tickets, one other tourist join us in the 4-bed cabin. Toilet is spacious and clean in the beginning of the trip. Water dispenser is available on train.
Push cart selling simple food and drinks is available at the beginning of the trip. There was ppl selling ticket for transit between Lao Cai to Sapa. Just be cautioned that there is no fixed vehicle and we need to look for one presumed person in charge to make the seating arrangement among few available vans and I saw a few ppl eventually need to be placed to take bus instead.
It has been an interesting experience to take a sleeper train to travel for us and given us more time to visit Hanoi and Sapa as the travel is at night. If you are a light sleeper then it may not be a good option though.
Review link: https://www.tripadvisor.com/Attraction_Review-g311304-d25070205-Reviews-VIC_SAPA_TRAIN-Sapa_Lao_Cai_Province.html