If I would offer a service like that (on Hive), I would just focus on grammaticality, spelling, and punctuations. I normally won't mind meaningless sentences like "colorless green ideas sleep furiously".
By the way, you just gave me an idea to sell services like that. :)
Glad I helped. While I can help (a lot) with Grammer, I'm not better than Grammarly Free myself, so I'm more helping in formatting, and advices to make the articles easier to read.
If I had premium Grammarly I would definitely sell the service.