Write I teach singing - gospel - acoustic - opera - basic voice production
I offer anyone who wants the chance to learn a free intro session so that if it is truly terrible they have not suffered financially

I think that one has to be very careful about comments about singing unless specifically asked I would not pass an opinion as negative comments can destroy someone's confidence
There is a difference between

1 Nervous trier who needs gentle encouragement and positive vibes in a constructive manner
2 The truly talentless which are far fewer than people think. Many voices can be rejigged by simply getting the person to sing in the right key or register
3 The bone idle who will not prepare IMO reading the words means the person concerned has not prepared the song and cannot sing it properly if they are reading from a text

I used to belong to writers groups and have sat through some gruesome sessions of authors reading their efforts. I would suggest each group or sing around has clear guidellines as to what expected in terms of basic performance level You know the words and the tune. or is that too much. The near enough for folk is not good enough and never was