There's no way to know who's going to be a bad or not specially if you don't care about a tool that well can help you weed out the worst offenders. Also sadly this game doesn't do a good job of teaching people how to do their job or about rotations and no you can't really use SSS as a marker because that just says they have enough dps to clear the fight while just standing there. You also will run into a lot of people who want to run savage or try their hand at savage who don't care and there's nothing you can do and sometimes even the game can't do to make them actually care about actually trying. Then there are those people who are bad because they don't know how to improve but are at least trying.