For the last year, their booking engine (on their web site) was working quite well and I had no pb to book tickets.
For bag rules, you'll find all info on their web site
http://www.cambodiaangkorair.com/en/...d-baggage.aspx
(From this page, info on checked bags and surcharges can be accessed from links on the left of the screen). What I can tell you is that the 20kg rule for checked bags is not strictly enforced. I have usually 23-24 kg and they never charged me.