We booked a few weeks in advance, paid a the 4th floor office in Marrakech. We arrived end of the afternoon to stay at Sahara services for 1 day in the end of september 2012. We were welcomed by the manager and could still choose which room we wanted to stay for the night, we could choose for 2 searate rooms of 1 bigger room. The room was air conditioned and clean. The food was good and well prepared. Lateron they started to play desert music and made fire. We had good company and a great evening.
However they won't tell you that much about the trip on beforehand you can always ask everthing you want to know. Our trip would only start at 16.00 the next day to the desert, while we were expecting to leave more early. But in the end we were glad we stayed in M'hamid a little longer. The manager took us to the old Kasbah in town to have another tea, which was a great experience. We even went to his families home to met his mother and sisters.
When we got back after 2 nights of desert there was no problem at all to take a shower at one of the rooms although we would leave within a few hours. They even prepared a small lunch for us when we were about to leave. They also helped us out to point us to the next garage to inflate our tires. We experienced a very flexible and friendly staff and would defenitely recommend the sahara services!
Wifi is available as well :)