Over the years.... very many years..... we occasionally allowed 'guest vocalists' to take to our mic's. It would have made a great youtube that would have undoubtedly gone viral.... think " people of walmart".
There were exceptions, however.... one I wrote about here on the Pub many years ago.... a lady who stepped up to the mic and stunned me and the rest of the band.... as good as I've ever heard. She could easily have sung professionally. After the gig I sought her out to tell her that very thing.... I found her... passed out just outside the front door to the saloon lying in a pool of her own vomit. I was told she always ended her singing performances in the same manner.