Constructive comments are helpful and productive feedback given to someone with the intention of providing suggestions or improvements instead of criticizing or being negative. Full definition
This edit includes changes you can make to improve your book as well as a general overview of your manuscript with constructive comments for improvement. (archwaypublishing.com)
As an author I welcome constructive comments — if a reader doesn't like my books I want to know why as much as those who did enjoy the read. (goodereader.com)
We always appreciate constructive comments which help us to maintain and improve our standards, as well as meet and exceed guest expectations. (palmcoveaustralia.com)