And the people of Berea were more open-minded than those in Thessalonica, and they listened eagerly to Paul’s message. They searched the Scriptures day after day to see if Paul and Silas were teaching the truth.
Acts of the Apostles 17:11 NLT

Do you believe something “because ____________ told me so”? Or because you read the Word of God, because you know the Word of God, because you search it out in the Word of God to either confirm it as truth or deny as a lie?

Dear friends, do not believe everyone who claims to speak by the Spirit. You must test them to see if the spirit they have comes from God. For there are many false prophets in the world.
1 John 4:1 NLT

Why is it important to test things by the Word of God and not just by pour own feelings, conscience or opinions?

You should know this, Timothy, that in the last days there will be very difficult times. For people will love only themselves and their money. They will be boastful and proud, scoffing at God, disobedient to their parents, and ungrateful. They will consider nothing sacred. They will be unloving and unforgiving; they will slander others and have no self-control. They will be cruel and hate what is good. They will betray their friends, be reckless, be puffed up with pride, and love pleasure rather than God. They will act religious, but they will reject the power that could make them godly. Stay away from people like that!
2 Timothy 3:1‭-‬5 NLT

Is the Word of God trustworthy and sufficient?

All Scripture is inspired by God and is useful to teach us what is true and to make us realize what is wrong in our lives. It corrects us when we are wrong and teaches us to do what is right. God uses it to prepare and equip his people to do every good work.
2 Timothy 3:16‭-‬17 NLT

What about those speaking their own opinions as opposed to speaking the Word of God?

The tongue can bring death or life; those who love to talk will reap the consequences.
Proverbs 18:21 NLT

And I tell you this, you must give an account on judgment day for every idle word you speak. The words you say will either acquit you or condemn you.”
Matthew 12:36‭-‬37 NLT

And do not just hear and speak the Word of God, but live accordingly by the spirit bit the flesh, if you indeed have Christ in you!

But when anything is exposed by the light, it becomes visible, for anything that becomes visible is light. Therefore it says, “Awake, O sleeper, and arise from the dead, and Christ will shine on you.” Look carefully then how you walk, not as unwise but as wise, making the best use of the time, because the days are evil. Therefore do not be foolish, but understand what the will of the Lord is.
Ephesians 5:13‭-‬17 ESV

So put away all malice and all deceit and hypocrisy and envy and all slander. Like newborn infants, long for the pure spiritual milk, that by it you may grow up into salvation— if indeed you have tasted that the Lord is good. As you come to him, a living stone rejected by men but in the sight of God chosen and precious, you yourselves like living stones are being built up as a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ. For it stands in Scripture: “Behold, I am laying in Zion a stone, a cornerstone chosen and precious, and whoever believes in him will not be put to shame.” So the honor is for you who believe, but for those who do not believe, “The stone that the builders rejected has become the cornerstone,” and “A stone of stumbling, and a rock of offense.” They stumble because they disobey the word, as they were destined to do.
1 Peter 2:1‭-‬8 ESV