It's up to the performer themselves to raise their standard. The drive has to come from within not from somebody telling them they aren't good enough.
yes and no,the club organiser,or resident,may be a good person to give tactful constructive criticism,to the aspiring floor singer.,if they ask for it or if they query why they are not given a floor spot.
Snail,what has the Lewes arms got to do with this?,other than your desire to publicise the club,that you are one tenth of the committee.