Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. 2 This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, 3 but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.
That's a fairly easy order for many modern-day prophets to meet; acknowledge the Incarnation.
However, you can meet that spec and still be well off the reservation. One example might be of this odd Happy Science Japanese mash-up that messed with the Ugandan Olympic Trials; the national stadium got double-booked and the track team wound up running on a slower track, costing Ugandan runners some qualifying times.
The Wikipedia for HS has their founder channeling Jesus as one of many of his predecessors; "Okawa claims to channel the spirits of Muhammad, Christ, Buddha and Confucius." That sounds a bit like Bahai's take of their prophets being God's Rep 6.0 and 7.0 to Jesus' 4.0 and Mohammad's 5.0. They might be able to pass the Incarnation test above, but not a broader spiritual sniff-test.
Where it gets tougher is where a preacher is orthodox on basics like the Incarnation but winds up losing it on secondary issues. There is a lot of room for heresy and leading people astray while not being read out of Christendom at first look.
Discernment can be abused word, running anyone off who doesn't agree with your detailed theology 100% in its more allergic form. We need discernment to make sure a preacher's take isn't his Saturday night wet burrito talking, but we also need to make sure our rejection of his take isn't our bratwurst from this afternoon talking. A faulty spiritual filter can let in bad stuff or reject good stuff.
That's where an ongoing relationship with God, including His Holy Spirit, is vital.