What we suggest for this process of negotiating and redlining is having the customer use the Comment button when they are reviewing the document to sign.
This button will open the document up in Google Docs. From there, the signer can use the Google Docs suggestions and comments features to suggest edits to the documents or leave comments.
You’ll be notified when others make comments/suggestions.
As the document owner, you can control the settings of the document to only allow others to make suggestions rather than directly edit the document.
All versions are saved in the Google Doc in revision history via the comment history feature. There is no downloading/saving, back and forth activity like with Word.
The leaving and resolving of comments/suggestions and all changes to the document occur in real time. Once everything is resolved, the customer can then just sign the document with the same link, since it leads to the (updated) document.