Are you reviewing the theme or just leaving a review because the “free premium offer” MyThemeShop setup instructed you to?
If you are taking advantage of that theme author’s “Premium” offer which includes instruction to leave a review, don’t you think that’s dishonest? Are you reviewing the theme or just attempting to get a commercial product the theme author’s offer?
That would not be a very honest review if it was just based on a commercial offer like that.