Since it was written it would be slander.
(Defamation is verbal.)

And whether it is slander/libel/defamation depends on whether the person stating it is stating falsehoods.

If the person making the statements is stating the truth – no defamation/libel/slander has occurred.

Otherwise Angie’s List and other rating services would cease to exist. Same with Yelp, etc.

Now if the statements are an outright lie – that’s actionable.

At least that’s how our attorney explained it to me when I posted some negative reviews and was accused of slander. I had the facts behind me so there was no case.