I agree with LDMartin’s response.
However, If you have your own administrative account on the site, each time you log into your own account, the posts will open in the editor you last used when you logged out. I have noticed when I go into a client’s site with their login I am often starting out in Visual Editor and have to do what LDMartin suggested to keep from messing up the code.
I am looking forward to trying some of the other workarounds, plugins mentioned. I do wrap some shopping cart code with Raw HTML tags with the Raw HTML Plugin on one of my accounts and that works well, but is not practical for the whole post because the client cannot access any of the content.
DD you were perfectly clear in your explanation…