i listen to a whole lot of preachers from different denominations too -- i have a long commute, an hour each way, and i play what i like to call 'sermon audio roulette' while i'm driving, listening to two random sermons a day on average. it's taught me not to just accept what preachers say but to scrutinize it -- because i hear pastors contradicting each other. so one kind of 'litmus test' i've developed is like you say, do they teach from God's word or not? and another is, do they believe that Christ is God or not? i've found that very useful, and i gotta say, sermons that don't have error in them seem rarer than i used to think they were, before i started listening to tons of them. it's just like you say, there are a lot of false doctrines out there, and a lot of people who really don't know any better because they've been taught them all their lives and never really looked at the Bible and as it's written, and thought about whether what they are hearing really matches up with it.