The Reformation churches in Holland and the rest of NW Europe have morphed into stinking synagogues of Satan.
How can you be sure you are right?
How can you be sure you are right?"
You are right. Certainly any group which departs from the Scripture will end in the sewer. Rome is a perfect example (pedophile priests, homosexual supporting universities, etc.). So, rocks and glass houses and all of that, my FRiend.
If you define "right" as adhering to the Scriptures, you have identified the biblical method...stick to the Scriptures not tradition.