Seat-in-coach means you join others on the same tour, and thereby the tour cost is considerably cheaper than a private tour.
Seat-in-coach tour is preferable by the travelers who have a low budget or traveling alone or in small group who wish to join a group tour and make new friends. It is popular among Beijing, Xian, Guilin and Shanghai etc.. It’s a great way to explore the city with limited time.
These tours are available on fixed dates all the year round. It’s conducted in one day or half day. Each morning, guide will pick up travelers in different hotels and then go to visit the major attractions together with other tourists. Groups are kept to about 10 passengers in a comfortable modern 22-seat coach with professional guide. Tour guide will stay with you for the entire time and gives you the best introduction about his city.

It's much cheaper than private tour.
Guide will contact with travelers in the evening to confirm pick-up time in the next day.
Guide will call travelers' room upon arrive their hotel.
It is not so flexible as a private tour, but you may have a lot of new friends coming from all over the world.