In our day and age, actually since the beginning of the church, false gospels are many and rampant. Humans are crafty idol makers and every time we believe and preach a gospel that is different from that of the Sacred Scriptures we are dishonoring the Lord. We are making God into our own image every time we don't except Him for who He is in Scripture - Sovereign and Holy. Changing His message, the gospel, to our liking is dangerous business, but many fall victim and as a result their participation in the Lord's mission becomes not just a hindrance but actually an obstacle to the church.
Here is a short clip from brother John Piper who does well at exposing one false gospel of our day - the "prosperity gospel" or "health and wealth gospel". I decided to share this clip after observing a random Facebook comment yesterday of a woman who really means well, but clearly does not have a biblical view of God and His gospel message. One of her comments was that when we come to God we will even experience financial blessing... Nothing could be further from the truth. For missions to be practical and God-honoring it is absolutely fundamental to have a clear understanding of what is God's message -what the gospel is and is not.