To be fiar, I only join LFG prestige Raids when the fireteam leader checks Raid report. I dont want to spend hours in a single raid when it can be done under one hour.
Dont get me wrong, I have sherpaed lots of people through their first clears, but in my experience 70% of all "newbies" never listen or execute the advice you give them, which is why I stopped sherpaing.
Prestige Raids are hard, and everything has to go smoothly.
Which is why I am a fan of raid.report. You can always trust what people say