I am required to find a way to share my entire Mac with a potential buyer, since there is a lot of code involved that we want to guard I need to find a way to share my Mac with them without them being able to either download or copy anything from my Mac and also unable to insert anything to my Mac - thus allowing them to only eye the various codes and systems we've created and even use them but not able to take any of the data in ANY manner. (this obviously includes copy pasting code and files) I was unable to find anything that will serve this purpose online. Also, if you can think of an alternative way of sharing a computer's content while having this restrictions that would also be great (something like git hub but that doeant allow copy or download). Any suggestions?
"Share" in what way?
You can screen-share in observe-only mode, but that wouldn't stop them making screenshots, even if it meant having to type it all out later.
The only real safe way is for you to be at the machine & them to be looking over your shoulder - look but don't touch - then all they would have is what they can remember about the session.
Anyone who has physical access to your machine has access to the data on it.
You could use parental controls or permissions to regulate file system access but Scott is right, there is no way to do exactly what you are asking. Maybe send them snippets of what you want to show them or fully compiled unpackable versions of your code?