Heresy is holding to an opinion or doctrine that’s at odds with established beliefs.
While the Christian church has arguably never been without heretical views throughout its history, some people worry that leaderless, self-governing, or laity-led groups are more open to false doctrine since they operate without the benefit of having trained clergy lead them. However, most major heresies in the past two thousand years have originated from trained clergy and not untrained leaders or egalitarian groups.
The church at Berea avoided the risk of heresy by studying what the Bible said to make sure everything Paul told them was true. Verifying what ministers teach is the best way to avoid going astray.
The groups most prone to heresy are those with dominant or proud leaders who squash all dissension. They often state, or at least imply, that their degrees make them right and therefore immune to heresy. But by disallowing question and dialogue, they remove an important check on their teaching and risk leading their people astray.
Regardless of what ministers tell us, testing all teaching against what the Bible says is the best way to avoid heresy.