So sorry for your loss!
I think Hulizack's suggestion to get a necropsy done is a very good one. Knowing why Ting died will give you some peace of mind. Even if you do find out it was your fault, you will at least feel better about your ability to prevent the same thing in the future.
I also agree with Michelle (BPElizabeth) that since it happened so soon after you got him, and the open mouth thing started even sooner, that the snake was most likely already sick when it arrived.
I would definitely contact the person you got him from, immediately so that he is aware what happened, and again after you get the necropsy results back. It is possible that you will be offered a replacement snake or a refund. However, I think the more important reason is to let him know to look for any possible issues on his end so they can be corrected.